Last night, Windows Live Events became available to the general public. If you've ever used Evite, then you're familiar with the Windows Live Events concept. You can use the site to plan events such as birthday parties, costume parties, farewell, parties, and there's even a template for planning a wedding by using the site, but I can't imagine that getting too much usage.
Since it's built on the Windows Live Spaces framework, it's very well integrated into the whole package of Live services. You can send invites to your Windows Live Messenger friends and others with a Windows Live ID. You can send invites to your friends without a Live ID as well, but they won't get the full experience. Such as the ability to upload pictures and videos of the event to the site after the party's over.
So if you've got a party coming up, and you're a Windows Live Spaces user, head on over and give it a try, it's free.