OpenSpades is described as 'open source OpenGL-based alternative game client by yvt that can be used to play on all AoS 0.75 and AoS 0.76 servers listed on BuildAndShoot.com. It's compatible with PySnip/pyspades and runs on Windows, Mac, and Linux'. There are three games similar to OpenSpades for Windows, Linux and Mac. The best alternative is Ace of Spades: Battle Builder. It's not free, so if you're looking for a free alternative, you could try TOpenSpadongs.