not exactly free, since isnt the free verison limited compared to other versions
From the free version you can release a full game on PC, Mac and on the web provided you make less than $100,000 a year from it. However once it's released there's nothing to stop you buying the pro version if you're making that much.
The restrictions are from mobile/console platforms (which you have to buy licences for) or if you want to use the more advanced features in Unity. Unless you absolutely
need one of the missing features, it's not a huge deal. The biggest ones are render-to-texture and post processing, but you can get some of that with custom shaders if you're willing to write them. Most of the rest is 'useful but not essential'.
There's a full comparison here:
http://unity3d.com/unity/licensesAnyway, my point is that you can do a lot of cool stuff with the free version and if you get it to a polished enough degree there's no reason you can't just release that without buying the pro version.
