If evolution was a jerk, who would win? Impossible Creatures is an RTS that lets you combine animals into monstrous new configurations, making it the only game that lets you find out what would happen you merged a whale with a scorpion and made it fight a tiger with the head of a hammerhead shark.
It's the missing link in Relic's back catalogue, and it's on sale on Steam now for £5.39 / $5.99, though I would pay as much again for a David Attenborough commentary pack.
Before you'd have to hunt on eBay or scour Amazon for a pre-owned physical copy, now it's been "fully remastered" by Nordic games to work on modern PCs, and includes the Insect Invasion DLC pack that adds six extra maps and 15 animals. Multiplayer has been "re-implemented" to hopefully work smoothly with modern NAT setups and the SDK is included for map makers.
This is the only Relic game I haven't played (apart from Xbox 360 exclusive, The Outfit), and I can't wait to try it. It was Relic's curious experiment between Homeworlds, before the studio went on to make Dawn of War and Company of Heroes. I'm not expecting it to quite match those classics, but I'll download any game that lets me order a flanking attack with a squadron of flying whales.