Lunchclub - Curated 1:1 professional connections
Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Serendipity - Serendipity is a PHP-powered weblog engine which gives the user an easy way to maintain a blog.
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Coworker Coffee - Coffee with a different coworker each week
Bigtent - BigTent is a web-based organization and communication portal for groups.