EssentialPIM - EssentialPIM is a free Personal Information Manager that keeps up with the times and lets you manage appointments, tasks, notes, contacts, password entries and email messages across multiple devices and cloud applications.

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

Todo.txt - Track your tasks and projects in a plain text file, todo.txt. A todo.

DownToMeet - DownToMeet is a platform to organize, find, and attend group events.

Task Coach - Task Coach is a simple open source todo manager to keep track of personal tasks and todo lists.

Mighty Networks - Mighty Networks enables entrepreneurs, organizations, and companies to create and grow a community-powered brand.