Recs.
Updated
i3 is a dynamic window manager that is targeted at advanced users and developers. It uses clean and documented code in order to allow for ease of configuration.
SpecsUpdate
Pros
Pro Easily readable plain-text configuration
i3 has plain-text configuration, meaning that no lua or haskell is needed. This makes it rather easy to recommend i3 to other people without worrying whether or not they have the knowledge to configure it as it can be read by anyone without prior knowledge.
Pro Excellent documentation
Every feature is thoroughly documented (including examples), and documentation is kept up-to-date. For questions that are not answered by the i3 user guide, because they concern tools outside of i3 for example, there is the community question & answer site.
Pro Can be reloaded quickly and configured without a client restart
Just two hot keys: Shift+Super+C to reload the config and Shift+Super+R to restart (which takes less than one second). Restarts pick up new versions of i3 or the updated config file, so you can upgrade to a newer version or quickly see the changes to i3 without quitting your X session.
Cons
Con Missing "include" possibility in config
While pretty good and easy to use for common tasks, the configuration language is missing the include
directive common in other languages. You can use a workaround - a shell script to config parts on demand. It would be best if this were built-in however.