Few things in the world of programming are as hot as GitHub. Boasting 4 million users, the code-sharing site boasts itself as the largest code host in the world. With 7.8 million repositories and counting, it's hard to argue.

Based on the Git software version control system engineered by Linux founder Linus Torvalds, GitHub has blossomed since its launch in 2008. From ABAP to Xtend, GitHub offers open source projects in almost every conceivable programming language.

Following is a roundup of the most popular projects on GitHub. Creators, contributors, and users weigh in on what makes these projects special -- and why GitHub is so vital to the development of both community and code.