How many second life games are there

There are two public Second Life platforms:
Second Life for adults over the age of 18
Teen Second Life (teen.secondlife.com) for teens ages 13-17.

There are other versions of the Second Life platform out there for various businesses, educational institutes, governmental agencies, etc, but these platforms are closed to the public and require special access. The Second Life teen grid was closed in January 2011 and is no longer available.