For work I’ve been looking into Calendar Servers to see what they are capable of doing in case we want to implement any.  We already have an active directory server and mail server, so some of the groupware servers might not be the best fit for us.  I’ve found four open source calendar server products, which I plan to research more:

• Apple’s Darwin Calendar Server
• Bedework
• Really Simple CalDav Store
• Cosmo

I hope to be able to post more here when I find out more.