For Linux and other X Window System based desktop OS, this Python script allows you to switch any given window through a keyboard shortcut, which is in most cases faster than mouse clicking or Alt-Tab.
This tool depends on the xdotool utility from X Windows (apt install xdotool for Debian etc).
Just save this file somewhere on your disk.
To switch to the Chrome brower or Emacs for examples, run
python window_switch.py chrome
or
python window_switch.py emacs
You can bind hot key shortcuts to these commands (in Gnome for example), so Ctl-Alt-G will switch to Chrome.