Information is a bit sparse on the page, so here is more information:

Source is available here: https://github.com/stevedekorte/Bitpost

This is a client based on the BitMessage protocol. Here is a whitepaper that describes BitMessage: https://bitmessage.org/bitmessage.pdf

What I would like to know (since it seems that the original developers are reviewing comments made here it seems): How is this different from PGP? (Wikipedia article in case you're reading this and haven't heard of PGP: http://en.wikipedia.org/wiki/Pretty_Good_Privacy)