I have read stories about people being jailed or even tortured and executed for expressing politically incorrect opinions at different internet sites (forums, blogs, twitter, facebook...). This issue applies both to "democratic" and totalitarian states, therefore people will benefit globally from a service where they can express themselves publicly and anonymously.
It is possible that such solution already exists that permits you to post public messages without the risk of revealing your identity (IP / email). Most services where you can participate in discussions will however track your IP and requires email for registration. I guess the closest you can come to an easy solution is Reddit+TOR but there should be an open source alternative that is even simpler and more secure to use.
So my suggestion is something like BitMessage, with some additional functionality.
-Encryption must be optional so you can post in a public forum
-Encryption is used to enable private forums
-Your identity is protected in the same way as BitMessage.
-Mechanism to prevent spamming (hashcash)
-Nodes must actively choose which forums they want to share
-Nodes can chose to only keep the last N days of messages for each forum to save disk space
-Entrepreneurs will create forum sites like Reddit based on this proposed "BitForum"
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Useful sources
https://github.com/Bitmessage/PyBitmessage
http://labs.bittorrent.com/experiments/sync.html
http://sourceforge.net/projects/p2pbackupsmile/11
https://github.com/tomp2p/TomP2P
https://code.google.com/p/openkad/
http://code.google.com/p/bitcoop/
http://www.i2p2.de/
http://syndie.i2p2.de/faq.html
http://www.opendht.org/faq.html
