It's been a while since Achron first appeared at GDC 2009, but the time-travelling/"meta-time" real-time strategy game is now available with a beta for Windows/Mac/Linux (full release coming in the third quarter of 2011).

If you're looking for a unique take on the strategy genre, Hazardous Software definitely has created something new with Achron:

"You can undo your mistakes, change your strategy after committing to it, preview the future, freeze time to perfectly coordinate attacks, and send entire fleets through time to when they are needed.

However, all of your opponents will also be independently moving across time, attempting to rewrite history in their favor."

If you preorder the game, you can start playing the beta now. This early build does not contain the single-player story-mode campaigns; it include "a handful of single-player demo and tutorial levels, as well as multiplayer levels."