LinkedIn - LinkedIn is a business-oriented social networking service, mainly used for professional networking.
Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Good.Co - eHarmony meets LinkedIn!
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
indeed - Find jobs using Indeed, the most comprehensive search engine for jobs.
Google Groups - Google Groups allows you to create and participate in online forums and email-based groups with a rich experience for community conversations.