iRacing is both an entertaining game where you race against others, and a training tool for the real life racers who contributed to its development. In April 2010, more than half of the current IndyCar series drivers were using iRacing for fun and training. What other online simulation games are worth playing? Tell us in the comments below.  Developed in 2004, iRacing lets you compete against others using officially licensed cars on  licensed replicas of the world's greatest tracks. Drivers race in different leagues, according to their skills and type of racing (fun or serious), and there are special contests with cash prizes, as well as championships. To get involved you need a Windows PC, broadband Internet connection and either a joystick, gamepad or steering wheel with pedals. There are various subscriptions, though the annual $99 fee seems typical. You can also try it for a month or pay for shorter periods. Tracks are laser mapped down to the millimeter to incorporate the right bumps, curves, camber, etc. The cars are modeled using physics engines for a realistic performance. Wikipedia says recent cars in the game have had their performance modeled through computational fluid physics.There are road tracks, and a high level of racing detail as well: Drivers need to consider tire heat build up, drafting and even telemetry output. iRacing had its first major upgrade -- to version 2.0 -- about a year ago. It added a new tire model and updated graphics. The game can handle 40 cars racing side by side and nose to tail, with drafting effects. Its creators have partnered with the Williams F1 team and automobile manufacturers including Ford, VW of America and GM. If your driving is not up to scratch you will get penalized. Drivers who practice safe driving progress faster than those who are unsafe. When you fork out more than $10 a month for the game, you might think it would keep out the people who deliberately try to crash into others, but apparently not. Compared to World of Warcraft or online combat simulations, driving simulations are something of a niche with far fewer players. However, iRacing has shown that these games can be done well. Related Links