Open-source clone of the original X-Com (source files)
openxcom_source-1.0-6-source
OpenXcom is an open-source clone of the original UFO: Enemy Unknown (X-Com: UFO Defense in USA), licensed under the GPL and written in C++ / SDL. It was originally founded by SupSuper in February 2010, and has since grown into a small development team surrounded by a very supporting community.