Bookmark It - Create awesome notes on YouTube videos
Calendify - Calendify is an event community where you can share, publish, and subscribe to event calendars. It helps you to stay informed about what you are interested in and what is yet to come.
Sidenote - Timestamped notes on YouTube videos
Vamos - Local Event Discovery
Video Search for YouTube - Search any YouTube video like a document.
Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.