Blue Mars is a 3D massively multiplayer virtual world platform. It falls in the general category of social virtual worlds allowing user-created content. The main web-site is here: Blue Mars
One of the features of Blue Mars is a framework that allows anyone to easily make bots. They are called Iams. Step-by-step instructions on how to make your own bot and inhabit it with your A.I. can be found here: Blue Mars A.I.
A couple of ready-to-run example bots can be downloaded here: Sample Bots
Some of them can be seen in action below.