Alien Arena: Tactical is still powered by the CRX engine, a heavily modified open-source code-base of early id Software engine code. Max of the Alien Arena project wrote in a media email to Phoronix, "Alien Arena 7.66 is going to be released in the next couple of weeks. This is a comparatively minor update-- besides some minor optimizations, the biggest change is a painfully overdue overhaul of our menu system (see attached screenshots.) The real news is that, accompanying this release, we are also releasing the alpha test of Alien Arena: Tactical. It uses the same game engine as Alien Arena, but it is a very different game. It is, of course, open source, and will remain open source forever, but the full version will be a commercial release."
Those curious about the upcoming Alien Arena: Tactical game can visit Desura.com for details or the Alien Arena Forums.