i3 is a tiling window manager, tiling window manager is non-overlapping frames of application windows. it will look like this

Installing on ubuntu GNOME/Unity:

sudo echo "deb http://debian.sur5r.net/i3/ $(lsb_release -c -s) universe" >> /etc/apt/sources.list
sudo apt-get update
sudo apt-get --allow-unauthenticated install sur5r-keyring
sudo apt-get update
sudo apt-get install i3

This will install i3wm in ubuntu. Now to switch to i3, logout of current session.

In login page, you can find circle icon above your user account, click on it and select i3.

When you login, it will immediatley ask you if you want to create an config file, press enter and generate a config file.

Generally Modifier key is "Windows Key".

Modifer+ Enter ---> open terminal.

you can now  use your windows tiling manager.

Bloatware:

If you're planning to only use i3, then most of you're applications useful in Ubuntu like nautilus..,etc becomes bloatware, so install ubuntu server image. Then use above commands to install i3wm, Also Install

# install display drivers
sudo apt-get install xorg

# start i3 
startx

This will start i3 manager by default since there is no other GUI modes (like gnome, unity, xcfe) ..etc.,