Well i don't know if you have heard of Torque Game Engine (http://www.garagegames.com) It is a $100 engine that is used to create games and stuff. 2 games i know of that are from this engine are Blockland (www.blockland.us) and Age Of Time (www.ageoftime.com) both by the same creator, go check the games out if you want some fun.
Blockland is a lego game (costs $20) and is a newer version of torque and you can play online with friends or w/e you can try the demo for fun.
Age of Time is a online game that contains only one server that you connect to and play with others, Some cool things the game has is jail thing were if you disobey the law you goto jail and wait a period of time (not much but depends on what you do and how many times you do it ) It also has fighting and you can get some cool items and stuff to help you become better, And it is a fps (First Person Shooter) This game doesn't take much at all to run and is barely any memory on your computer.
So go check the games out, And if you want the older version of blockland (free one) goto www.sithous.com (my site) and get it. also there is Age of Time version 3 (lets you make servers and host unlike the v28 one)