Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.
i3 - A dynamic tiling window manager designed for X11, inspired by wmii, and written in C.
Notion - All-in-one workspace. One tool for your whole team. Write, plan, and get organized.
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.
Slack - A messaging app for teams who see through the Earth!
Openbox - Openbox is a highly configurable, next generation window manager with extensive standards support.