PlaneShift

PlaneShift is a Role Playing Game immersed into a 3D virtual fantasy world which is Open Source and FULLY FREE to play. Fully free means you will have no surprises of premium content which will limit your gameplay or unbalance the game. PlaneShift is a non profit organization and is actively seeking developers for bringing the game to the next level of quality and fun!

Minimum system requirements: 

CPU: 2.4 GHz
RAM: 1024 MB
GPU: OpenGL 1.4-compatible with 64MB VRAM
HDD: ~1.0 GB