A new OpenRA release was tagged recently, 20121019, which brings Dune 2000 mod support, dedicated server handling, UPnP support for multi-player, improved logic, new map editor tiles, four new RA units, new community made RA maps, RA balance changes, and much more.
This open-source RedAlert engine implementation currently supports Command & Conquer and Red Alert. Interestingly, OpenRA is implemented in C# using .NET/Mono and OpenGL. This Mono-based engine allows for native support on Windows, Linux, and Mac OS X.
This new release of the GPLv3-licensed engine comes six months after its earlier release. More details can be learned at the OpenRA project site.