GMail also support Calendar functions.
1. Press "Add event info" in top right angle of GMail box
2. Insert link to KML or KMZ file in field "Where"
3. Add time of event and other information.
4. Send this "geo event" to friends.
Your friends can add this event into Calendar, open KML in GE or GMaps.
PS Also see test Calendar with "geo events" in Googlepages