Hula does webmail right now and that's about it.
The calendering stuff is still advanced beta as I understand/heard it. But I'd bet that the progress is very rapid.
I REALY want to play around with it, though. I wouldn't put it into production just yet though.
You see Novell had web-based mail setup for a while now called NetMail They've been working on it for years and finally just took a whole bunch of code and created Hula...
The nice thing about it is that it will be extendable. Also you'll have clients that would be able to hook up to it, for instance a Email client will be able to check e-mail and use Caldev to interact with the calendering software. The extensions should be nice and people will create cool stuff like hooking VoIP and such.
But it's going to be a while from now before you get all the features going.
Best to download it and try it out and see how much is completed so far...