A new popular sandbox indie game to recently emerge is Terraria, described as similar to Metroid and a little like Minecraft. The game has been built by the small indie team Re-Logic and has sold a reported 50,000 copies since its release only a few days back.
Its own description - Dig, fight, explore, build! Nothing is impossible in this action-packed adventure game. The world is your canvas and the ground itself is your paint.
Terraria Recommended System Requirements
OS: Windows Xp, Vista, 7
CPU: 1.6 Ghz
GFX: 128mb Video Memory, capable of Shader Model 1.1
DirectX: 9.0c or Greater