Bitmessage is a P2P communication protocol used to send encrypted messages to another person or to many subscribers. It is decentralized and trustless, meaning that you need-not inherently trust any entities like root certificate authorities. It uses strong authentication, which means that the sender of a message cannot be spoofed. BM aims to hide metadata from passive eavesdroppers like those ongoing warrantless wiretapping programs. Hence the sender and receiver of Bitmessages stay anonymous.
Bitmessage is a collaborative project. You are welcome to submit pull requests although if you plan to put a non-trivial amount of work into coding new features, it is recommended that you first solicit feedback on the DevTalk pseudo-mailing list: BM-2D9QKN4teYRvoq2fyzpiftPh9WP9qggtzh
Feel welcome to join chan "bitmessage", BM-2cWy7cvHoq3f1rYMerRJp8PT653jjSuEdY which is on preview here: http://beamstat.com/chan/bitmessage