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

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

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

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

Strikethru - Strikethru is a kind of to-do list notebook for managing work lists and staying updated with the important tasks.

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