Ask Slashdot: Open Source Calendaring

buzz lightyear asks: "I'm trying to find out about developments in RFC2445 - Internet Calendaring and Scheduling...and RFC2447 - Internet Calendar Messaging. Can you tell me what the state of play is regarding these functions? eCommerce is starting to require such connectivity, irritating though that may be..and I want to find out where the developments are, if any. Needless to say some propriatary system will fill the gap if left open long enough."