So what's OpenRA?
OpenRA is a cross-platform Libre/Free Open-Source Real Time Strategy game engine. It is a highly moddable recreation of the early Westwood games. In fact both Red Alert and Command & Conquer are implemented purely as mods on it.
Fork us at GitHub or download the binaries and get ready for epic internet matches! Get new maps and units for your mod at OpenRA ressources. Join the chat at #openra on Freenode IRC. Find answer at the wiki.