The final release of Planetary Annihilation isn't expected until year's end for all major platforms, but Uber Entertainment is keeping the Linux developments in-step with OS X and Windows. Thus, available now is the alpha release of Planetary Annihilation for Linux gamers.
This game is developed largely by the teams that also created the Total Annihilation and Supreme Commander games. The game started as a Kickstarter campaign. Its web-site describes the title as "[bringing] Real-Time Strategy to a new generation of gamers in a way that’s never been seen before- taking large scale real time strategy games from the past to gameplay on a planetary scale."
When writing last year that this game would come to Linux, it excited many Phoronix readers and led to lots of discussions in the forums. Now with the alpha game being out, there's also screenshots to see and other information being shared.