I3 (window manager)

i3 is a tiling window manager designed for X11, inspired by wmii and written in C. It supports tiling, stacking, and tabbing layouts, which it handles dynamically. Configuration is achieved via plain text file and extending i3 is possible using its Unix domain socket and JSON based IPC interface from many programming languages.
Like wmii, i3 uses a control system very similar to that of vi. By default, window focus is controlled by the 'Mod1' (Alt key/Win key) plus the right-hand home row keys (Mod1+J,K,L,;), while window movement is controlled by the addition of the Shift key (Mod1+Shift+J,K,L,;). 
Floating pop-up windows.
Even though i3 is a tiling window manager, specific windows, such as password pop-ups, are not displayed as new tiles by default; they are always stacked in front of tiled windows, unless in full screen mode. These floating windows can be moved and resized freely, just as they can in popular desktop environments like GNOME or KDE Plasma.
The authors of i3 intend floating windows to be used for pop-up windows only.