Todo.txt - Track your tasks and projects in a plain text file, todo.txt. A todo.
Mighty Networks - Mighty Networks enables entrepreneurs, organizations, and companies to create and grow a community-powered brand.
Task Coach - Task Coach is a simple open source todo manager to keep track of personal tasks and todo lists.
Bigtent - BigTent is a web-based organization and communication portal for groups.
Strikethru - Strikethru is a kind of to-do list notebook for managing work lists and staying updated with the important tasks.
Nabble - Nabble is a forum software that are embeddable and fully customizable with scripting language.