Google Groups - Google Groups allows you to create and participate in online forums and email-based groups with a rich experience for community conversations.
Joplin - Joplin is a free, open source note taking and to-do application, which can handle a large number of notes organised into notebooks. The notes are searchable, tagged and modified either from the applications directly or from your own text editor.
DownToMeet - DownToMeet is a platform to organize, find, and attend group events.
OneNote - Get the OneNote app for free on your tablet, phone, and computer, so you can capture your ideas and to-do lists in one place wherever you are. Or try OneNote with Office for free.
Mighty Networks - Mighty Networks enables entrepreneurs, organizations, and companies to create and grow a community-powered brand.
Standard Notes - A safe place for your notes, thoughts, and life's work