Racing simulation service iRacing.com has come to the Mac. iRacing features subscription-based, massively-multiplayer online racing in multiple leagues, including NASCAR, IndyCar, and Williams F1. Subscriptions starts at $12 per month. The OS X version of iRacing.com is the same as the PC version, and is compatble with the Snow Leopard, Lion, and Mountain Lion releases of OS X. Addtionally, Macs will need to be using Intel HD Graphics 4000 or better, 2GB of RAM, and 6GB of hard drive space to run the service.
Below is a video detailing iRacing.com's service.