Group Calendar 5.0 is finished! The final release version is available in the forums or from curse.com or wowinterface.com. A huge thanks to the many players and guilds who helped testing through the beta cycles and for all the great feedback.
Look for 5.1 soon with “maybe” signups and the ability to tweak settings like disabling the tradeskill or other reminders. I plan to have it ready for patch 3.3.