There are several free games available on Steam that are compatible with Mac. Some popular options include "Team Fortress 2," "Dota 2," "Warframe," "Path of Exile," "Brawlhalla," and "Unturned." These games cover a range of genres, so you're likely to find something that suits your interests.

Luckily, there is a way you can run PC games on your Mac. The easiest is by installing Windows on your Mac. To do so, you can use Mac's Boot Camp, but this would mean rebooting your computer each time you want to play your game.