SmallDevTools - Handy developer tools with a delightful interface
Google Open Source - All of Googles open source projects under a single umbrella
LaunchKit - Open Source - A popular suite of developer tools, now 100% open source.
Opensource Builders - Find open-source alternatives to commercial apps
TextLab - TextLab is the fastest way to format, prettify, transform, hash, encode, and decode your data instantly!
GitHub Student Developer Pack - The best developer tools, free for students.