Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Poptop UK - Extraordinary private party experiences and services - private chefs, mobile bars, BBQs, food vans and more!
Google Groups - Google Groups allows you to create and participate in online forums and email-based groups with a rich experience for community conversations.
PromoTixApp - PromoTix is the world's first and only free online ticketing platform for events. Use PromoTix to create and ticket events, market events, and monetize your live stream event with secured and ticketed unique URLs online to the world.
Bigtent - BigTent is a web-based organization and communication portal for groups.