iCal Core Spec - RFC2445. Personal Telco uses the phpiCalendar app which works great - it displays iCal files in HTML. it has no editing abilities. Lots of our members are very command line savy. It be great to have a command line utility that makes inserts/updates/deletes to an iCal file.
Which leads me to think we'd be better off with an XML Calendaring Schema. It'd be easier to transmit, modify, and verify.