Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Disciple - Grow, engage and monetise your community with Disciple community software. Get your own branded community platform on Web, iOS and Android
GroupSpaces - Free Group Website, Membership Database, Listserv Mailing List, Online Group Management Software : GroupSpaces
Forumotion.com - Create a free forum : free forum hosting, free forum skins, templates editing, chatbox, RPG mod... Choose PhpBB 2 - 3, Invision or PunBB. Create forums now!
The Groups Place - The Groups Place is a new alternative to Meetup.
Proboards - ProBoards is a host of free forums with customer service.