For those of you who like to design abstract games, the online abstract game site igGameCenter has a tool for designing them which allows you to play prototypes of abstract games online in realtime, either publicly or privately.
http://www.iggamecenter.com/
http://www.iggamecenter.com/info/en/sandbox.html
I have found it extremely useful.
More on igGameCenter here:
http://nickbentley.posterous.com/the-beauty-and-wonder-of-iggamecenter