Popper is a minor-mode to tame the flood of ephemeral windows Emacs
produces, while still keeping them within arm's reach.  Designate any
buffer to "popup" status, and it will stay out of your way.  Disimss
or summon it easily with one key.  Cycle through all your "popups" or
just the ones relevant to your current buffer.  Useful for many
things, including toggling display of REPLs, documentation,
compilation or shell output, etc.

For a demo describing usage and customization see
https://www.youtube.com/watch?v=E-xUNlZi3rI