Web-based Calendar software?

Has anyone had any experience with good free web-based calendar software?
Preferably using PHP? (I've been teaching myself PHP lately)

Here's what I'd like...
-Web-based so I can access it from anywhere.
-Ability to send an email to me to remind me of upcoming events.

I'm not looking for a service like Yahoo or anything. I'd like to run this from
my own servers.

Thanks,
~M