Full discussion here
A bit of a non-standard post as I don’t think you can actually play them for free yet (I can’t see any binaries available and there’s a disclaimer that you need to already own the games, presumably for assets/art), but a pleasant surprise and hopefully something to keep an eye on!
Actually, you can play for free C&C, Red Alert and, iirc, Tiberian Sun. EA released them all for free some years ago so you can find their ISOS anywhere legally