We are using the Unity3D version, which supports Linux. So it should be a walk in the park to get Planet Explorers working on Linux. We don't have a Linux system lying around to test on, that's why we're not being definitive about it. But you can be sure the game will support it when it comes out.
To play Planet Explorers, you'll need an OpenCL compatible graphics card. You can go here and take a look at this list: http://www.phaseone.com/Search/Article.aspx?articleid=1720&LanguageID=1 Beyond that, any CPU from the last 3-5 years will do, and 3GB+ of ram, preferably DDR3.
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