Battle Monkeys is a free multiplayer game for the MacBook and iMac that tries to hook you with its gameplay into buying upgrades. The installation is quick as a download from the App Store. There are both single-player and multiplayer games available online.
When launched, the game displays some excellent graphics, offering a simple tutorial to explain the game mechanics. Essentially, monkeys sit on your various keyboard keys. Each turn you can jump to any of the two keys available in any direction. Your goal is to try and kill the monkeys before they kill you. Some keys have special capabilities that affect the other monkeys on the keyboard. Those special keys change each turn. Gameplay takes only a minute to learn, and the variability of the special keys makes playing dependent on luck.
Some players will get into Battle Monkeys by trying all the different monkeys available. Others will buy upgrades (typically spending about $10) to try and gain additional advantages over their opponents. You also can customize the way your monkeys look, although that doesn't affect the game in any way we found. The graphics and soundtrack are excellent, but we did get a bit bored by the basic gameplay after a few minutes. Even after buying some of the special upgrades we didn't get hooked. Battle Monkeys will appeal to some casual gamers, but you are advised to try the free version for a while before purchasing upgrades.