Off topic: class calendaring software

[Dr. Greg Quinn]

Hi;
Yep, this is a little off topic; has anyone who frequents 
this newsgroup written or know of software that enables
students to sign up for a class or meeting online? This is
nothing to do with online teaching, but rather to enable 
people to register for a class that would have a limited 
capactity. I've written something but it's not scalable.

Thanks for your thoughts
Greg