Lunchclub - Curated 1:1 professional connections
Levels.fyi - Compare career levels across software eng and other fields
Serendipity - Serendipity is a PHP-powered weblog engine which gives the user an easy way to maintain a blog.
Caliber - IM for LinkedIn. Instantly chat with your business contacts.
Lunch Roulette - Collaboration by grouping coworkers randomly for lunch.
whoishiring.io - Making the IT job search simpler and more effective