Minimum:

OS:Windows XP SP3 (for Version 1.11, accessible through the 'Betas' tab)
Processor:Intel Core 2 Duo 2.8Ghz or equivalent
Memory:2 GB RAM
Graphics:2nd Generation Intel Core HD Graphics (2000/3000), or dedicated GPU with OpenGL 3.0 Support
Hard Drive:500 MB HD space
Sound:OpenAL-compatible
Additional:See https://getsatisfaction.com/polytron/topics/support_for_intel_integrated_graphics_hardware for details on Intel HD Graphics support, not all models are supported. Latest graphics drivers are required to maximize OpenGL feature compatibility.

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