Tungle is a free meeting coordinator that lets people:

Share your availability
View the availability of friends, colleagues or business associates before sending them a meeting invitation.

Coordinate meetings with anyone
Create Tungle Spaces - temporary web sites for coordinating meetings with anyone, including people who don't have Tungle.

Use your existing calendar
Get started in seconds, using your existing calendar, including Outlook, across firewalls and organizations.

Source: Tungle, via Techcrunch