B2gdroid is an experiment that let you use the user interface of FirefoxOS (Gaia) on your Android device.
The name b2gdroid is a reference to Boot2Gecko, the basis of Firefox OS. Basicly b2gdroid is a launcher, but it comes also with several apps and you can even go to the FirefoxOS Marketplace and download an app.
B2gdroid comes with an on-screen Home button, sadly in this version the hardware buttons don’t work well. Hopefully this will be solved in the next version(s).
If you want to give b2gdroid a try, you can download an APK (only ARM support) here.