OpenXcom is one of those projects I've been following religiously, not only because I'm a huge fan of the X-COM series, but also because it promised to deliver a fully stable and bug free engine port released under a Free Software license.
The last time I talked about it, it seemed like there was still much work to be done, but apparently things have changed, as the developers suddenly just went from a fairly incomplete version 0.4 to a fully playable and enhanced version 0.9.
This is obviously great news to all X-COM fans. OpenXcom now ensures the game can be ported to practically every modern device or OS you can think of. It also allows improved mod support and further enhancements to gameplay and graphics to be made by the community. Sadly the infamously hard sequel to X-COM, known as Terror from the Deep, is yet to be supported, something that will hopefully change in the upcoming versions of OpenXcom.
You can download OpenXcom v0.9 here.
The engine requires an original copy of X-COM: UFO Defense/UFO: Enemy Unknown in order to run, which can be purchased here.
Finally, if you're interested in modding or downloading mods made specifically for OpenXcom, you should check this page.
Code License: GPLv3