The games getting a source code release are Command & Conquer (Tiberian Dawn), Red Alert ... You can find them all on EA's Github page. As for the Steam Workshop? That's getting switched on ...

Command & Conquer - Combined Arms is a huge free RTS game based on OpenRA that includes Command & Conquer and Red Alert ...

The atmosphere of Warhammer 40k, the grueling RTS gameplay of Command and Conquer, and even grand strategy systems meet in Dust Front.

(Plus, never forget that Red Alert 3 also contains the single best line delivery in all of video game history.) EA released meticulous remasters of the first two installments of Command & Conquer ...

EA just released source code for a bunch of old Command and Conquer games, and added Steam Workshop support to bangers like C&C 3: Tiberium Wars ...