Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Hive - Seamless project management and collaboration for your team.
GroupSpaces - Free Group Website, Membership Database, Listserv Mailing List, Online Group Management Software : GroupSpaces
Sup! Standup Bot - The complete stand-up and follow-up bot
The Groups Place - The Groups Place is a new alternative to Meetup.
Asana - Asana project management is an effort to re-imagine how we work together, through modern productivity software. Fast and versatile, Asana helps individuals and groups get more done.