OpenRA is a open source recreation of Westwood's unnamed 2D game engine(s). Currently playable are Red Alert, Command and Conquer: Tiberian Dawn(C&C95), and Dune 2000. Tiberian Sun is in the works, but don't hold your breath.These are not 1:1 copies of the originals. There are some changes in each game, the one I am experienced with is Red Alert so I will note a few changes.
-Helicopters can now hover in place instead of landing on the ground, they only need to land to reload or repair.
-Allies get helicopters (Chinook, Hind, Longbow), soviets get planes. (Yak, Mig)
-Artillery have more range and now out-range a Tesla Coil.
-Demo Trucks are soviet-only.
A feature currently being tested is a radius around the Construction Yard that limits how far you can expand from it(you can always move your MCV or build another), this is to prevent what is known as "base walking" which was a cheap tactic(if you can even call it that). A player would build a line of power plants or other cheap buildings across the map to their enemies base along with base defense buildings which is difficult to counter. Every game came down to players base-walking into each other.
I hope you will give this game a try, not too many players around unfortunately. I suggest downloading the last stable release and not the current playtest.
Even more, I hope some talent will find the time to help make OpenRA a better game by contributing on GetHub.