I was wondering if it is possible to have items grouped in list like this:
http://martinleslie.files.wordpress.com ... -stack.jpg
or in a rectangle area like this:
http://u1.ipernity.com/1/70/08/907008.48d47b4c.560.jpg

I have looked after a module doing this, or an item, or something else, but I couldn't find anything at all.

That's called Stacks and is currently not supported, although it is high on the to-do list. Nexus Ultimate supports something similar called 'sub-docks' tough, and you can have as many sub-docks as you want, and even nested sub-docks.

You can also use Cris'n'Soft's 3rd party stand-alone Stacks, if you want.

Please note that when native Stacks support is finally added, it will most likely only be available in Nexus Ultimate and not the free version of Nexus.