One of the best-loved Command & Conquer titles of all time is 100% free of charge on Origin.
As a part of the company’s ‘On the House’ promo, which runs just about quarterly, the alternate history RTS Red Alert 2 is free to download and keep. Even better, you’ll also get the Yuri’s Revenge expansion pack, which was pretty good if I remember correctly. No strings in place for this, or for anything that’s a part of On the House, as EA just basically gives these titles away.
All you need to take part is an Origin account, which is also free mind you, and you’re golden. As for how long it’ll hold that ‘free’ status, you probably have some time to add it to your collection, but really- why wait?