Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Virus Cafe - Make a friend in 2 minutes
Event Hunt - Startups and Tech Events Curated By Locals
Upto App - A shared calendar to share and organise your plans with your friends.
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Serendipity - Serendipity is a PHP-powered weblog engine which gives the user an easy way to maintain a blog.