These are all groups on Meetup.com within a 50 mile radius of zip 30309 in Midtown Atlanta which list "Tech" as the primary category, sorted by number of members.
This was pulled from the Meetup API using https://github.com/FokkeZB/Meetup.
- Atlanta Web Design Group - October 8, 2002 - 3230
- The Online ColdFusion Meetup - May 14, 2004 - 2764
- Atlanta HTML5 User Group - August 16, 2011 - 2500
- The Atlanta JavaScript Meetup Group - February 5, 2009 - 2265
- Data Science ATL - May 23, 2012 - 1963
- Atlanta Mobile Developers Group - September 22, 2009 - 1934
- The Atlanta iOS Developers - January 14, 2008 - 1889
- Freeside Atlanta - April 3, 2012 - 1842
- Atlanta Scrum Users Group - May 12, 2008 - 1780
- Atlanta Ruby Meetup Group - September 12, 2006 - 1758
- Atlanta WordPress Users Group - September 12, 2008 - 1733
- PyAtl: Atlanta Python Programmers - December 19, 2002 - 1616
- Atlanta Wordpress & SEO - October 2, 2011 - 1526
- Atlanta Bloggers - July 21, 2008 - 1481
- AtlantaPHP Meetup Group - June 10, 2006 - 1267
- Atlanta Big Data User Group - May 1, 2012 - 1198
- Nerd Fun - Atlanta - July 22, 2009 - 1026
- Cloud Computing Atlanta - October 31, 2010 - 1012
- IxDA Atlanta - August 15, 2012 - 944
- Atlanta Java Users Group - August 17, 2012 - 941
- Atlanta User Experience Group - April 9, 2009 - 939
- The Atlanta Game Developer Meetup Group - April 7, 2006 - 887
- Atlanta Hadoop Users Group - April 27, 2009 - 877
- Atlanta Android Developers - December 25, 2009 - 867
- DevOpsATL - September 17, 2010 - 844
- Atlanta Web Technology Group - February 3, 2009 - 840
- Atlanta Nodejs Developers - November 10, 2011 - 787
- The Atlanta Drupal User's Group - April 5, 2007 - 779
- Atlanta Startup Founder 101 - October 2, 2013 - 766
- Women Who Code - Atlanta - June 27, 2013 - 721
- Atlanta .Net User Group - July 30, 2013 - 680
- TRC Presents Web Development Classes - August 29, 2012 - 675
- Adobe User Group of Atlanta - June 5, 2011 - 675
- Atlanta Developers - ADEV - August 9, 2011 - 625
- WordPress Hands-On Learning Group - May 10, 2011 - 615
- All Things WordPress - N. Atlanta Group - March 26, 2012 - 606
- The North Atlanta iOS Developers Group - January 28, 2011 - 606
- AMDEV - Atlanta Microsoft Developers - August 17, 2011 - 603
- Internet Marketers of Georgia - April 2, 2009 - 602
- ALT.NET Atlanta Pragmatic Programmers - July 11, 2008 - 575
- Atlanta Software Craftsmanship - October 25, 2010 - 563
- Association of Black Engineers, Scientists and Tech - November 9, 2007 - 554
- Business Intelligence Society of Atlanta - January 2, 2010 - 550
- Atlanta MongoDB User Group - March 26, 2011 - 532
- Atlanta OpenStack Meetup Group - February 21, 2012 - 531
- Gwinnett Georgia Microsoft Users Group - August 13, 2011 - 527
- Atlanta Spring User Group - March 24, 2010 - 526
- Big Data Processing & Analytics - HPCC Systems (LexisNexis) - August 18, 2011 - 508
- Joomla! User Group Atlanta - March 19, 2008 - 486
- The Atlanta SEO Meetup Group - April 12, 2005 - 476
- Atlanta Internet Marketers - August 19, 2007 - 470
- The Iron Yard - Atlanta - May 8, 2014 - 467
- Atlanta Web Performance Group - August 3, 2011 - 437
- Atlanta Salesforce Developer Group - August 14, 2012 - 434
- Code for Atlanta - June 5, 2014 - 421
- AWS Atlanta - December 30, 2013 - 420
- Atlanta R Users Group - February 14, 2012 - 405
- Girl Develop It Atlanta - August 13, 2014 - 393
- OWASP Atlanta - December 26, 2011 - 391
- GA 400 Linux Group - August 23, 2012 - 385
- Google Developer Group Atlanta - May 31, 2013 - 378
- Atlanta Internet Video Marketing Association Meeting - June 25, 2010 - 375
- The Atlanta MySQL Meetup Group - December 22, 2006 - 362
- Decatur Makers - July 11, 2013 - 360
- Big Data Developers in Atlanta - March 8, 2013 - 359
- Docker Atlanta - October 15, 2013 - 358
- Geekspace Gwinnett - May 3, 2012 - 357
- Atlanta-Lean-Startup-Circle - January 24, 2011 - 350
- Tech Talent South - Atlanta - July 17, 2014 - 346
- Social Media Atlanta - January 28, 2010 - 331
- Rails Girls Atlanta - December 5, 2012 - 328
- The Business Intelligence SIG - November 8, 2013 - 321
- Enterprise App Development - January 19, 2014 - 321
- Atlanta Titanium Developers - March 27, 2012 - 309
- Metro Atlanta Bloggers - July 11, 2014 - 303
- Atlanta Microsoft Business Intelligence Users - August 27, 2012 - 298
- The Atlanta Scala Meetup Group - June 18, 2009 - 297
- Intro to coding in Java (free) - Alpharetta - November 27, 2014 - 285
- Atlanta Mobile Marketing Organization (AMMO) - September 29, 2009 - 282
- MobileCity - August 21, 2012 - 270
- WordPress Gwinnett - February 4, 2012 - 260
- Atlanta Windows Apps - October 2, 2012 - 258
- CoderDojo Ponce Springs - May 7, 2013 - 257
- AlphaRetta Ventures & Incubator - January 15, 2013 - 253
- BarCamp Atlanta - August 20, 2009 - 243
- Atlanta Data Visualization and Infographics - August 27, 2012 - 240
- amUX - August 22, 2014 - 225
- Hacks/Hackers Atlanta - November 8, 2010 - 225
- Code Sharks (Learn to Code the Easy Way!) - August 26, 2013 - 223
- Sensors and Startups - February 18, 2014 - 222
- ATL Digital Rendezvous - January 14, 2014 - 218
- Splunk Metro Atlanta User Group - September 3, 2012 - 218
- PyLadiesATL - August 9, 2012 - 216
- CHI*Atlanta - User Experience Professionals - September 19, 2013 - 214
- Atlanta Unity 3D Developers Meetup - January 30, 2014 - 211
- Atlanta Sitecore User Group - May 29, 2012 - 211
- Atlanta Cassandra Users Group - May 15, 2012 - 211
- A Bunch of Devs - January 23, 2013 - 207
- Atlanta Xamarin Users Group - April 26, 2013 - 205
- MoMo Atlanta (Mobile Monday Atlanta) - January 6, 2014 - 202
- Go User Group Atlanta - May 2, 2013 - 201
- Learning “Machine Learning” by Example - October 23, 2012 - 199
- South East Puppet User Group - November 28, 2011 - 196
- Cobb County Makers Meetup - April 7, 2014 - 193
- Atlanta Unix Users' Group - May 28, 2012 - 193
- Social Media For Business - Atlanta - January 2, 2014 - 193
- Atlanta WordPress Professionals - September 5, 2010 - 193
- Unicorn Invasion - July 14, 2014 - 192
- GeoDev Meetup Group - Southeast - November 18, 2010 - 191
- Atl-Clj - April 27, 2012 - 190
- Atlanta Food Bloggers' Alliance - September 24, 2010 - 190
- Meteor Atlanta - February 21, 2013 - 185
- ATL-JBUG - October 10, 2011 - 185
- Content Strategy Atlanta - August 22, 2013 - 182
- Ladies That UX ATL - September 2, 2014 - 177
- Atlanta Big Data Science - October 13, 2014 - 173
- Make & Build's Geek Nights - July 3, 2012 - 173
- Southeast Information Technology Professionals - April 29, 2013 - 172
- General Assembly - August 5, 2014 - 170
- UX Book Club Atlanta - February 13, 2013 - 165
- The Atlanta WordPress Coder's Guild™ - December 8, 2014 - 160
- Atlanta Windows App Developers - January 22, 2013 - 160
- CoderDojo McDonough - January 24, 2014 - 158
- Analytics Club Atlanta - Big Data to Discovery - November 19, 2014 - 156
- The Atlanta Macintosh Users Group - March 3, 2010 - 154
- North Atlanta Startup Coffee Meetup - September 12, 2014 - 152
- Atlanta Java Concept Pros - November 29, 2012 - 151
- Atlanta LGBT Tech - October 17, 2014 - 150
- Metropolitan Atlanta Geospatial Society - January 4, 2011 - 147
- Atlanta MEAN (Mongo, Express, Angular, Node) Developers - September 1, 2013 - 147
- Graph Database - Atlanta - December 18, 2012 - 145
- Azure in the ATL - October 6, 2014 - 144
- New Media Marketing Alliance - April 13, 2006 - 143
- Business-Side of Web Design: Sales and Marketing Insights - February 26, 2013 - 143
- The Atlanta ColdFusion User Group (ACFUG) - May 23, 2011 - 139
- Magento Developers - October 7, 2010 - 136
- Alpharetta PHP/Laravel Group - February 26, 2013 - 131
- Atlanta Cloud Foundry Meetup - October 6, 2014 - 129
- Quantified Self Atlanta - May 23, 2012 - 126
- Ember.js Atlanta Meetup - July 23, 2012 - 125
- Atlanta Informatica User Group - August 27, 2014 - 123
- Apache Spark - February 13, 2014 - 122
- ARAtlanta: The Atlanta Augmented Reality Meetup - March 15, 2011 - 121
- The Atlanta NetSquared Meetup - February 22, 2007 - 121
- TechieChic - Atlanta - April 21, 2013 - 120
- Intro to coding in Java (free) - Atlanta - January 10, 2015 - 118
- BDPA ATLANTA - November 2, 2014 - 118
- Atlanta iOS Study Group - April 21, 2013 - 117
- Atlanta Analytics Meetup - March 15, 2013 - 116
- North Atlanta Digital Creatives - February 27, 2013 - 116
- Founders' Roundtable - April 2, 2013 - 115
- Atlanta SEO Meetup | Hosted by Everspark Interactive - December 4, 2013 - 115
- Technology Association of Georgia - September 30, 2014 - 112
- Atlanta Network Programmability User's Group (NPUG) - December 2, 2014 - 108
- Atlanta Selenium/Watir WebDriver Meetup - July 8, 2013 - 108
- Duluth WordPress Users Group - June 13, 2013 - 108
- Kanban - Atlanta Limited WIP Society - May 29, 2012 - 104
- uCode@UWG - July 25, 2014 - 101
- Smyrna Technology Initiative - October 3, 2013 - 98
- Internet of Things Atlanta - January 10, 2014 - 93
- Atlanta MicroStrategy User Group - April 28, 2013 - 90
- Atlanta Sass Meetup - @ATLSass - October 16, 2014 - 88
- Atlanta Developers Unit (ADU) - January 22, 2015 - 88
- Atlanta Lync Users Group - February 27, 2013 - 87
- Atlanta Mobile Application Security - January 20, 2014 - 87
- Atlanta Alfresco Content Management User Group - August 3, 2009 - 86
- Atlanta PC Users Group - October 10, 2012 - 84
- North Atlanta AngularJS User Group - February 2, 2015 - 82
- Atlanta CRM - October 27, 2014 - 80
- Atlanta Mobile Marketing Meetup - January 16, 2012 - 78
- Build Guild Atlanta - September 8, 2014 - 77
- Alpharetta Rails Coders - September 17, 2014 - 77
- Atlanta Mobile Design Meetup - January 15, 2015 - 76
- Atlanta Apache Lucene/Solr Meetup - July 9, 2014 - 76
- South Atlanta WordPress Users Group - February 28, 2013 - 75
- Product Hunt Atlanta - Where new products are discovered - November 7, 2014 - 75
- Atlanta Google Apps Meetup - October 16, 2013 - 73
- Huge Atlanta - March 17, 2014 - 72
- Elasticsearch User Group - Atlanta - June 10, 2013 - 72
- DevOps OTP ATL - July 15, 2013 - 71
- Atlanta Famo.us Meetup - September 8, 2014 - 70
- Verizon Cloud Hackathon Atlanta Meetup - October 30, 2014 - 70
- Atlanta Lisp User Group - July 16, 2010 - 69
- BuildLabAlpha Makerspace - June 25, 2013 - 69
- Atlanta YouTube Video Meetup Group - August 10, 2011 - 66
- North Atlanta Data Science - September 26, 2014 - 66
- North Atlanta Salesforce.com Meetup - August 17, 2014 - 66
- Unite with Suzanne Atlanta eCommerce Meet Up - November 30, 2014 - 65
- Roswell WebDev Mentorship & Social Initiative - September 3, 2014 - 65
- Kids 4 Coding - November 4, 2014 - 65
- Atlanta Cloud and Big Data Meetup - September 16, 2014 - 64
- Atlanta Groovy and Grails User Group - July 7, 2013 - 64
- Wearable Technology | Atlanta Designers, Developers & Makers - July 11, 2013 - 63
- SharePoint Technology Meetup - Alpharetta Johns Creek - January 12, 2014 - 62
- Atlanta Erlang Users Group (ATLEUG) - September 8, 2011 - 62
- Atlanta Product Management Meetup - September 29, 2010 - 62
- Society for Technical Communication Atlanta - Meetup - January 10, 2014 - 61
- Automated Testing Atlanta @AutoTestCentral - February 26, 2014 - 60
- Afterwerk™ - February 25, 2014 - 60
- The Atlanta Cisco Technology Group - April 21, 2014 - 59
- The Atlanta Semantic Web Meetup - July 16, 2009 - 59
- MoDevAtlanta - August 12, 2013 - 55
- Makerspace Forsyth - September 4, 2014 - 52
- Atlanta Riak Meetup - April 2, 2013 - 51
- Northern GA MEAN Meetup - January 28, 2015 - 50
- AITP Atlanta - Association of IT Professionals - February 6, 2014 - 49
- Scaling Agile Atlanta - March 31, 2014 - 48
- McDonough Makers - October 15, 2014 - 48
- Atlanta Cloud Computing Meetup - August 4, 2014 - 48
- Atlanta In-Memory Computing Meetup - January 22, 2014 - 48
- Atlanta Internet Of Things - June 9, 2014 - 47
- Atlanta Jaspersoft User Group - May 4, 2012 - 46
- Atlanta Accessibility Meetup Group - June 23, 2009 - 45
- Atlanta PowerShell User's Group Meetup - November 19, 2014 - 43
- Kirkwood Makers - January 4, 2015 - 43
- Atlanta Ionic Developers - February 7, 2015 - 42
- Atlanta Elixir Meetup - September 9, 2013 - 41
- PostgreSQL in Atlanta - December 10, 2014 - 40
- UX Mentors Meetup - March 14, 2014 - 40
- Atlanta Bluemix Girls' Night Meetup - November 7, 2014 - 40
- MaptimeATL - October 16, 2014 - 40
- Atlanta WebRTC Meetup - January 26, 2015 - 39
- Ceph Atlanta - March 29, 2014 - 39
- Atlanta Laravel Group - January 19, 2015 - 38
- Southeastern Inventors Association - August 26, 2014 - 37
- Atlanta Growth Hackers - November 19, 2013 - 37
- Ultimate Frisbee Meetup for Developers - October 21, 2014 - 37
- Kirkwood WordPress User Group - July 29, 2014 - 37
- The Intersection of Business and Software Development - July 24, 2014 - 37
- Georgia Digital Innovation Incubator Meetup, by Software AG - November 10, 2014 - 36
- Startup Jobs - January 25, 2011 - 36
- Atlanta SaltStack User Group - April 8, 2014 - 36
- Alpharetta D3.js Explorers - September 28, 2014 - 36
- Atlanta Hobby Robot Club - October 28, 2014 - 35
- Lean UX of Atlanta - August 18, 2014 - 35
- ATLANTA 3D group - May 15, 2014 - 35
- Atlanta DAM - June 20, 2013 - 31
- [parents of] Kids Who Love Programming - June 19, 2014 - 30
- Tintri Atlanta - Smart Storage for VMware, Hyper-V and RHEV - May 19, 2014 - 30
- Breaking Bottlenecks in an Agile Setup - September 10, 2014 - 30
- PMP Certification Meetup - Suwanee Alpharetta - GA - September 20, 2014 - 30
- Google Marketing Agency Meetup - December 3, 2014 - 30
- SugarCRM Atlanta - October 27, 2014 - 28
- Atlanta Startup Engineering Leadership - February 17, 2014 - 28
- Corona SDK - Atlanta Meetup - May 22, 2012 - 28
- Atl Unreal Developers Meetup - October 16, 2014 - 28
- Business Intelligence Data Visualization Mastermind Group - March 4, 2014 - 27
- Cisco Networking Group - June 25, 2014 - 26
- South Atlanta Linux User's Group - August 30, 2012 - 26
- Iterate Atlanta - April 16, 2014 - 25
- VersionOne Developer Users Group - January 15, 2014 - 24
- Atlanta Community Managers Meetup - January 27, 2015 - 23
- Devoxx4kids SATL (South Atlanta) - January 27, 2015 - 23
- The Microsoft Meetup Group - Atlanta - September 4, 2014 - 23
- Ping Identity User Group - Atlanta - March 21, 2012 - 22
- Reality Computing Atlanta - May 22, 2014 - 22
- Peachtree City Makers: 3D Printing, Arduino & Robotics - February 3, 2015 - 21
- Podcast Atlanta - February 15, 2015 - 21
- Atlanta Salesforce Nonprofit User Group - January 19, 2015 - 21
- Bluemix-Developers-in-Atlanta - April 15, 2014 - 21
- Forecast Atlanta - Sales & Technology Leaders of the Future - January 29, 2014 - 20
- Kevy Connects - Atlanta - August 29, 2013 - 19
- Atlanta Automated Testing Meetup - January 26, 2015 - 18
- Connected Black Professionals - January 9, 2015 - 17
- Trestor Connect - Atlanta Chapter - December 24, 2014 - 17
- Functional Swift Study Group - February 1, 2015 - 17
- Atlanta Microsoft Cloud - February 7, 2012 - 17
- Atlanta's Collegiate Developers - April 16, 2014 - 15
- Atlanta Area Cognos TM1 Warriors - March 14, 2013 - 15
- IT Computer Helpdesk (ITCH) - February 13, 2014 - 15
- Setting up Website + Social Media for Startup Retail Busines - November 3, 2014 - 15
- Atlanta AppDynamics Meetup - January 23, 2015 - 14
- The Atlanta Sitefinity Meetup - August 12, 2014 - 14
- Atlanta New Relic User Group - February 10, 2015 - 13
- Arista Networks Atlanta Area Group - February 12, 2015 - 13
- Atlanta Connected Device Developers Group - January 26, 2013 - 13
- North Atlanta Podcasters - July 7, 2013 - 13
- Wordpress Northeast Georgia - August 6, 2014 - 13
- FileMaker Atlanta - March 20, 2014 - 11
- Cigital Atlanta - October 12, 2012 - 11
- Metro Atlanta Data Connectors - August 14, 2013 - 10
- STEM-AB - July 12, 2012 - 10
- Atlanta Latino Tech Group - February 12, 2015 - 9
- Metro Atlanta Home Automation - March 22, 2012 - 9
- Atlanta Video Surveillance Meetup - September 15, 2014 - 9
- Solution Accelerator - May 21, 2014 - 9
- PrestaShop Meetup -- Atlanta - October 5, 2012 - 7
- Atlanta FileMaker Pro Users Group - September 13, 2013 - 6
- Apache Kafka ATL - February 23, 2015 - 5
- Private Label Product Mastermind Group - Atlanta - February 21, 2015 - 2
- Refresh Atlanta - July 13, 2014 - 1
- [New Name Coming Soon] Sports Technology Group - March 11, 2014 - 1
- Georgia HP 3PAR Users Group - February 11, 2015 - 1