Google Groups - Google Groups allows you to create and participate in online forums and email-based groups with a rich experience for community conversations.

Tribe.so - Tribe is a white-label platform, empowering the new generation of online communities.

Galette - Galette is a membership management web application towards non profit organizations.

Higher Logic - Private, secure online communities that stimulate conversation and ignite engagement.

Bigtent - BigTent is a web-based organization and communication portal for groups.

Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.