By far the best open world survival game on the market.. 2nd is Empyrion.
Ark with expansions for $16.73 or get game or expansion for $10 each from steam!
As a man or woman stranded naked, freezing & starving on a mysterious island, you must hunt, harvest, craft items, grow crops, & build shelters to survive. Use skill & cunning to kill, tame, breed, & ride Dinosaurs & primeval creatures living on ARK, and team up with hundreds of players or play locally!
OS: 64-Bit Windows 7 Service Pack 1, or Windows 8
Processor: 2 GHz Dual-Core 64-bit CPU
Memory: 4000 MB RAM
Graphics: DirectX10 Compatible GPU with 1 GB Video RAM
DirectX: Version 10
Storage: 40000 MB available space