Multiwinia is pretty much a modified Darwinia made for Multiplayer. Some of the controls have been changed here and there but otherwise everything remains the same from Darwinia. There are multiple gamemodes and games can have up to 4 players. The map selection is surprisingly large for a game of this size but you can only play certain maps on certain gamemodes. As for gameplay the best experiences I've had for this game is playing with 3 or 4 people due to how chaotic things get towards the midgame. In Multiwinia there are these crates that drop down that grant either boons, such as units, reinforcements, or gun emplacements, and etc; or fuck you over. for example: by spawning in NPCs that target everyone including you. This can be edited in the settings but can be turned off completely if you hate fun. Sadly, like Darwinia, the playerbase is pretty much non-existent and died off a long time ago. I used to have a few buddies I'd play the game with but I'm not in contact with them anymore and literally no one I know currently knows about this game or is really even interested in giving it a try.
Also the soundtracks for Darwinia and DEFCON are kino and I've had them on my PC for years