Web Development

Collaboration
- Code Share
Date/Time
- Online Timestamp Converter
- Milliseconds since Unix Epoch
Editor
- Edit Pad: online text editor & wordpad for notes.
Encoding/Decoding
- encoding/decoding
HTTP
- httpbin.org: A simple HTTP Request & Response Service.
- Web Sniffer
- SOAP Client
JSON
Markdown
- Markdown editor
Regular Expressions
- Rex V: an Ajax regular expression evaluator.
- Regex Tester: A regex tester from Dan's Tools.
- RegExr: Learn, Build, & Test RegEx.
Testing
- eval.in
UI/CSS
- Colorblind Web Page Filter.
URL Parsing
- URL Decoder/Encoder
- URL Parse
XML
- XML Schema Validator

Network

explainshell.com: Write down a command-line to see the help text that matches each argument.
keep a changelog: Don’t let your friends dump git logs into changelogs.
Read the Docs: Read the Docs simplifies software documentation by automating building, versioning, and hosting of your docs for you.
tldr: Simplified and community-driven man pages.
PDF
- Stirling-PDF: Locally hosted web application that allows you to perform various operations on PDF files.

reveal.js: A framework for easily creating beautiful presentations using HTML.
- reveal.js-plugins: Plugins for reveal.js.
- reveal-code-focus: A Reveal.js plugin that allows focusing on specific lines of code blocks.
showcode.app: Create beautiful, detailed code screenshots to share your code in the most appealing way. Created by Steve Bauman.
diagramming
- diagrams.net: diagrams.net is open source, online, desktop and container deployable diagramming software.
- Visual Paradigm: makes diagramming simple, with a powerful diagram editor, and a central workspace to access and share your work.