Miner Wars 2081, a game that nods directly to classic shooter Descent, has been out for a couple of months now. The 6DOF (6 degrees of freedom) space shooter has recently been updated with: an offline single-player campaign (previously a constant internet connection was required) and a variety of fixes and tweaks (details here).
Most interest is the two new add-ons that have been made available. Cheats gives players infinite ammo and immortality, whereas 2.5D Experiment is a 2.5D multiplayer add-on.

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