Google Groups - Google Groups allows you to create and participate in online forums and email-based groups with a rich experience for community conversations.
Missive - Team communication app now supporting FB, Twitter & SMS
Galette - Galette is a membership management web application towards non profit organizations.
Mailtrim - Email lives forever!. Reinvigorate your emailing experience with the best free email client, the Mailtrim
Bigtent - BigTent is a web-based organization and communication portal for groups.
Spike - Spike solves businesses' communication chaos by bringing together email, team chat, collaborative docs, and meetings, into one feed.