Thunar is a lightweight file manager with a very light memory footprint, a less cluttered layout and pretty much all the features one needs in a file manager!

Installing Thunar does not remove Nautilus so feel free to try it and see if you prefer it.

Installation
You can install Thunar using Add/remove, Synaptic, Ubuntu Software Centre or the good old fashion terminal: –

  • sudo apt-get install thunar

Once installed you can launch it from the Applciations > Accessories menu.

How To Set Thunar As Default File Manager
If you decide that you like using Thunar and would prefer to use it for browsing your files and folders, you can set it to be used instead of Nautilus.

Download the following script to your Home folder

  • http://dl.dropbox.com/u/1115768/defaultthunar

Make it executable

  • chmod +x defaultthunar

run the script
./defaultthunar

Switching back

To revert back to nautilus as default file manager simply run the script again: –

  • ./defaultthunar
Source:-
https://help.ubuntu.com/community/DefaultFileManager