i3 - A dynamic tiling window manager designed for X11, inspired by wmii, and written in C.
Streaks - The to-do list that helps you form good habits.
awesome - A dynamic window manager for the X Window System developed in the C and Lua programming languages.
Taskful - Deadlines, meet your match.
dwm - dwm is a dynamic window manager for X. It manages windows in tiled, monocle and floating layouts. All of the layouts can be applied dynamically, optimising the environment for the application in use and the task performed.
ToDoList - Windows desktop application to stay on top of your daily tasks.