I think cube2 or Sauerbraten would fit into that category. There's also Platinum Art Sandbox or something that was built off it. If you find one, they will probably have links to the others made from it. Another option might be to contact Unity and see if you can download an older version. I read somewhere that they do that. Genesis 3d is a pretty dated engine. The Blender Game engine is kind of along those lines also. The free version of 3d Gamestudio might work, too. Personally, though, I would contact Unity first and see if you could download an older version so when you upgrade, you'll have more useful skills. Unity is getting accepted more and more as a small indie engine as far as the web plugin goes. Kongregate just made a deal with them, which makes it a standard almost like Flash. Otherwise there may be a way to upgrade your video card. From my experience, it's hard to get people to trust in a small game download, so having a web portal or a common web plugin is something to think about.