This mod mashes up five factions from Command and Conquer's past into one giant brawl

pcgamer.com:

Soviets, Allies, GDI, Nod, and the Scrin: Five factions from the history of Command & Conquer that franchise fans can't help but recognize. There's one problem: They're spread across two different series—the Red Alert games and the Tiberian universe. Since 2018, one mod has sought to do the unthinkable: Smash 'em all together into one big, vicious brawl.

Command & Conquer: Combined Arms is just that mod. Complete with singleplayer missions, cooperative multiplayer missions, and the crown jewel of C&C, multiplayer skirmish, Combined Arms uses the OpenRA engine to recreate factions and units from the spectrum of C&C titles in stretching all the way to Tiberian Sun and Red Alert 2. Soviet Kirovs? Absolutely. GDI Titan mechs? Yes. The Grand Cannon? For sure. It also updates the original Command & Conquer timeline factions with the upgrade trees that the Red Alert games introduced—stuff like Tech Centers, Support powers, and Navies.

Combined Arms released an update just last week that adds a whole pile of new features, artworks, and sounds. It's frankly glorious stuff if you grew up on the pixelated tanks and FMV era of RTS games, watching units from games separated by years of time. They've also integrated an entire unit update system to enable you to retrofit existing units 

It's absolutely wild, to be honest, that this frankly ancient engine supports this on modern hardware. But it does, because the team developing OpenRA—a free and open source version of the original Red Alert engine—have put in thankless hours to enable others to have fun. (I'm going to also comfortably say that the released to the public work which went into Command & Conquer Remastered came up here too.)

Go ahead over to Moddb and download Command &