If you have not heard, Blue Mars is a new virtual world using current state of the art tech, described as a Next Generation Virtual World. It will be along the lines of Second Life, with significant differences. It is in Beta now and at the end of August the Beta will expand to a larger more open Beta. Tools for learning to build within Blue Mars are available now.
One of the bigger differences is content creation. Property rights are supposed to be better protected. Builders are more controlled. There are 3 levels of builders/creators, City, Block and Content. It seems a City builder is somewhat like the SIM/Region owner in Second Life (SL). A Block creator is more like a Parcel Owner in SL. Blue Mars (BM) block builders are restricted by the city builder they lease or rent from. Pricing to join any of these groups has not been released.

