Mixin.com – Calendar Sharing with Friends
Mixin is an online social-calendar application that allows you to share your agenda with your friends and tell them where you will be, and what you’ll be doing at any specific time in the future. You are able to post these agenda updates from your current calendar application, by email, SMS, IM or via Twitter.
Compare your agenda to your friend’s ones and propose a time to meet or a group activity based on when they are all free. For example, if you’d like to go out to dinner with your friends, check when they will all be free and then suggest a time and date. Your friends will be able to see your invitation and respond in the negative or the affirmative.