Wenboi is a GameBoy emulator written in C++. It's mostly a toy project for learning about emulation, but it aims to be usable somewhere in the future.
You can get the code via git from the repository just typing
git clone http://slack.codemaniacs.com/git/wenboi.git
in your command line :)
You can also browse the repository with GitWeb
I've set up a project page at ohloh.net for wenboi: