Actiontext - Todo.txt client for Windows 10
Task Coach - Task Coach is a simple open source todo manager to keep track of personal tasks and todo lists.
California - California is a new calendar application for GNOME 3. It's currently under heavy development.
todotxt.net - A minimalist, keyboard-driven Windows GUI for your todo.txt file
Effitask - Effitask is a graphical task manager, based on the todo.txt format.
Todo.txt - Track your tasks and projects in a plain text file, todo.txt. A todo.