It will largely depend on the version of Gnome that you're running:
In Gnome2, compiz is the way to go (with the grid plugin). For example, if you press
numkey-left the active window will occupy the left 50% of your screen. If pressed again, it will ocupy 2/3 of your screen. And if pressed a third time, it will occupy 1/3 of your screen.
Apparently compiz isn't compatible with Gnome3 though, so you'd have to stick with whatever shell extensions can replicate.
I haven't tried any of these yet, but here goes:
- gnome-shell-grid extension - Apparently tries to mimic the behavior from compiz, but I find no mention of it handling screen thirds (only halves are mentioned).
- gTile extension - Seems very customizable.
- Put Windows extension - Apparently very simple to use.