OmniOutliner - OmniOutliner is a writing app for collecting information, outlining ideas, adding structure to any sort of writing.

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

Dynalist - Dynalist is a web app that lets you break down and organize your thoughts in the format of lists.

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

Outlinely - Indispensable information organization tool for knowledge workers.

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