Meet-O-Matic - a simple meetup or schedule tool without needing to sign up to a complex calendar or event service. If you need to schedule a meeting tick the available dates on the calendar. An email is sent to your recipients from your special Meet-O-Matic email address, with the URL to the proposed meeting dates.
Recipients click on their invited URL and tick their availability, the sender will see a matrix of availability, you can even mark important people, and the system will recommend the best date.I’m not sure if recipients can also see each others availability.
Also see ipolipo and TimeBridge for Outlook…or just let others know your presence with Yatam.
Jaxtop - a cross between a webtop and desktop widgets