I've visited them a while back and tried some of their car, boat and F1 sims. Good stuff, they also had smell as a dimension in one of them. Can't say it felt as good as LFS at the time, but haven't tried since.
I remember a small sim "Racer" from a decade ago and had to check out if you really meant http://racer.nl/
It always seemed like a neat techdemo but went anywhere beyond that. There was not much to do except drive around by yourself and content was limited.
I vaguely remember we once tried 1v1 multiplayer on LAN, not sure if it worked.
You could download cars and tracks from the forums but it was often super buggy and you had to match the correct versions etc. Beyond the physics everything felt very incomplete.
Interesting that they make commercial simulators now.
For me it was one of many tech/physics demos that I loved to play around with at the time, no matter how buggy or half-finished. (Another project I remember is "Rigs of Rods")
Yes it is Racer but highly reworked out especially on the physics side ( a lot of bugs have been addressed).
The demo contains two cars. A formula student and a generic sedan. They are both excellent and you can race them. The driving is very natural and to be fair I prefer it to LFS. Really impressed.
The problem is the lack of cars and tracks and this makes it quiet useless.