Remember that old turn-based tactics series named XCOM a.k.a. UFO? Back in the early '90s it was one of the best and culminated with the masterpiece XCOM Apocalypse. The spiritual successor to this series, the new UFO After... (Afterlight, Afterglow, Aftershock a.s.o.) tried to revive the spirit of the old days, but is still flawed with bugs and conception errors. Now, a team of enthusiasts developed a real successor the XCOM, named UFO Alien Invasion, and are releasing it as freeware at:
http://ufo.myexp.de/
It is fully turn-based and goes against the current trend of CTB (continuous turn-based). This is how the XCOM series was devised in the first place and it really catches the spirit of the original. BTW, the project is still under development and looks really promising.
Hope you will enjoy it.