root@kali:~# apt-get update
root@kali:~# apt-get install git build-essential autoconf pkg-config # fresh systems only
root@kali:~# apt-get install i3 # to get dependencies
root@kali:~# mkdir gui && cd gui
root@kali:~# git clone https://www.github.com/Airblader/i3 i3-gaps
root@kali:~# cd i3-gaps
root@kali:~# autoreconf --force --install