"A full-featured, hackable tiling window manager written and configured in Python" - Qtile Website
SpecsUpdate
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Pros
Pro Hackable ecosystem
With easy writing your own widgets or extensions, hooks you can make it powerful integrated system. Dmenu friendly environment. Easy scriptable even with bash by qtile-cmd. Nice keybinding cheet sheet generator
Pro Extensible
It's easy to write your own layouts, widgets, and built-in commands.
Pro Written and configured entirely in Python.
You can leverage the full power and flexibility of the language to make it fit your needs.
Pro Free and open-source software.
It's distributed under the permissive MIT license.
Pro Active and growing community
There's always someone to lend a hand when you need help.
Pro Interactive
The commands you use in the Qshell (built in shell for interacting with the window manager) has an intuitive filesystem-like feeling, while staying so close to Python syntax you can basically paste it into your config file. And the best part, if you don't like Qshell, just use Your shell. qtile-cmd exposes all of Qtile's functionality to the console.
Cons
Con Doesn't handle errors well
As Qtile uses python, it crashes upon errors instead of handling it gracefully ( like in awesomwm).