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.
Mighty Networks - Mighty Networks enables entrepreneurs, organizations, and companies to create and grow a community-powered brand.
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.
Bigtent - BigTent is a web-based organization and communication portal for groups.
Standard Notes - A safe place for your notes, thoughts, and life's work
Nabble - Nabble is a forum software that are embeddable and fully customizable with scripting language.