Here are some useful Google Apps Script scripts which you can copy and deploy through Google Drive.
I may add to this in the future. Please open pull requests if you have your own scripts you want to add.
Note: The scripts for sending emails will not work on a large scale (especially if deployed through free Gmail accounts) as there are limits of how many emails you can send, which you might hit quite quickly.
(Optional) Take a look at this corresponding blog post to see how to use GAS and this repo.
This script acts as a HTTP Post endpoint and sends an email from your gmail address, when you provide it with a recipient address, subject, and HTML body.
This consists of 2 scripts. One sets a value in a Google Spreadsheet to true or false, the other simply retrieves the value. Both act as HTTP Endpoints.
This has a variety of uses. For example, when I want to turn on my PC when I'm away from home, I can use my phone to set the value to true. I have a raspberry pi which calls the retreive endpoint regularily. As soon as it sees a 'true', it sets the value back to false and sends a Wake on Lan packet to my PC to turn it on. (This avoids forwarding a http port to my pi)
Single script AppendLog.js acting as HTTP endpoint. Receives data using a HTTP Post parameter with key data. Appends the submitted data to a new line in a Google Spreadsheet.
Useful for application telemetry (collecting usage information within an application).
If you want to put a contact form on a static website, where you can't post the values to a php/node/go/dotnet backend, post the values to this Google Apps Script endpoint instead. It will log all entries in a Google Spreadsheet, and send you an email whenever someone submits something.
There is also code for using Google's ReCaptcha. I only provide the Google Apps Script code and assume you can figure out the client side code yourself.
Similar to the above example, if you want a 'subscribe to our mailing list' option on your static website you can use these endpoints instead. All email addresses submitted get logged on a Google Spreadsheet (without repeating any).
All scripts are released under MIT license so you can use them for anything you like, for both personal and commercial use.