We’re looking for a web based calendar program that would integrate with Outlook, Apple iCal, iPhone, and iPod Touch. These links make it seem like Google Calendar would work well.
http://lifehacker.com/5048189/five-best-calendar-applications
http://lifehacker.com/399407/how-to-sync-any-desktop-calendar-with-google-calendar
I use iCal Server, which technically can run for free on Linux although I haven’t succeeded in doing so yet. But the OS X Server version is easy enough if you have a test license around (cough cough). The thing I like about it is that I can create multiple calendars within one account, which Google will not do. So I can categorize and add colors, etc. But it does involve rolling my own. I’ll see if I can get gentoo to run it yet.