This is another one of those things I've not been able to discuss, but LiveSide reports that Microsoft inadvertently posted a beta version of Windows Live Calendar temporarily over the weekend. It's coming soon, let's just leave it at that.
After what seems like ages, Windows Live Calendar is almost out there. Windows Live Calendar was indeed up for a bit, for testing, and will be going live in a public beta VERY very soon, but it's not up yet. You can learn more about Windows Live Calendar here.
Related: First look at Windows Live Calendar