bsmerge is a dirty hack that was conceived in order to relieve a Raspberry Pi running Gentoo from having to compile ebuilds all by itself - a task that it most certainly was not designed for - but rather delegate this task to an Android phone or any other machine that builds packages faster than your Pi.
You can read more about the idea behind this programm in my blog, located at http://aspgluval.wordpress.com/.
This program is currently pre-pre-alpha, and not recommended for everyday use, however I've used it to compile quite a few packages for my Pi.