Wireflow is free, online and open sorrce tool for creating beautiful user flow prototypes. No Photoshop skills required!

Githubdocs is an open source application to easily generate a beautiful and responsive documentation website in minutes. Githubdocs can generate a documentation website either from static Markdown files or a remote Github repository.

Devhints is a set of useful cheatsheets displayed in a stylish way

Insight.io for GitHub is a browser plugin for GitHub that enables you to navigate and search through repositories like it's in your IDE