Anybody try this yet?
<a href="http://www.racer.nl/" target="_blank">Racer</a> is, well, a racing sim...

It uses (or wants to use) real life physics and has nice, shiny looking cars. It's available for Linux, Windows and whatever, but for OSX too! It's hardly a stable port and takes some work to get running but it's Open Source and free! With downloadable tracks and cars to boot!
Anyway, I'll tell you a bit about my (short) experience with it. I own an iBook 500 Mhz so YMMV
First off, after not getting it to work initially I read up a little in the insidemacgames link quoted on the page. Downloaded a new track and the Racer.app version someone provided and revved it up. It worked! Honda S2000 driving down the 2002 Zandvoort race track, actually a ten minute drive from where I live IRL. Controlling the car was a bit awkward, using the trackpad for throttle and steering, but I got around the Tarzan bend alive and well. Where the track splits into the old and the new part I took a right onto the new part. Touched the white line and fell through the world
I got to force quit it before it brought down the iBook, like it had done a few times before. Actually, touching any white line at low speed resulted in the car flopping wildly through the air and eventually sinking through the surface of the track. On the other hand I had no trouble getting out from under the guard rail in that same Tarzan bend at a more decent speed...
After starting it up again I ran a few laps on the old, disused track with no problems. Disregarding the awkward controls the car felt pretty natural, diving on the brakes and sliding nicely to the outside of a corner when powering out of it. I think it would be quite drivable using a decent controller.
Framerates were low, 20+ fps while standing still, 5+ while driving, but, as I said I have a puny iBook...
All in all, if you're a driving games freak like me, keep an eye on this project. It looks pretty good and handling (I guess) is pretty realistic. It's still very unstable (read very, VERY unstable), but definately has potential.
BTW: haven't tried the online feature yet so I don't know if that works...
cheers, ro