Where Bitcoin uses proof of work, spaceoin uses proof of server space as mining. What you do is store data for a disributed p2p internet, and the more data you store and successfully serve, the bigger your mining rate is.
This p2p internet is called MaidSafe. I have not yet had enough time to fully digest the technology, but to me it looks like if they manage to make it work as described then it will bring a paradigm shift.
I am impressed with how they have replaced all the top layers of the old infrastructure including DNS.
http://blog.maidsafe.net/