Mail Admins: What's Your Favorite (Free) PHP Webmail Program?

I’m looking to replace my SquirrelMail install with a diffrent package. I like RoundCube, but it’s still in beta and, while nicer than SquirrelMail (better design, slicker functionality), it’s still not as useful. I’ve looked at IMP, but I’m not sure I want to install the Horde framework just to play around with it–at least, not without hearing, first, what others have to say.

So, if you have a favorite webmail program, what is it? I’m looking for something that will connect to my mail backend using POP3 and IMAP, but I’m willing to look at a program if it only uses IMAP.

Since I’m running a Windows server, I could also look at .ASP programs, but I’d really like to focus on something OS agnostic. Any suggestions?

Bumpity bump-bump-bump.