Cinnamon is a Gnome-Shell desktop fork. It is not strictly a Gnome-2 interface, although the developers aims are laudable - to produce a simpler more traditional desktop interface.

Development seems to be rapid. It is usable and certainly fun to play with with a growing number of extensions to install to extend the base installation.

How to install

for 13.04 & 13.10, 14.10 & later

Cinnamon is now available in the Universe repository

cinnamon

Alternatively - from the command-line:

sudo apt-get install cinnamon-desktop-environment

Since it is in this repository, it is community maintained and thus it is up to the community to update the packages as and when new releases and bug-fixes are released.

For Ubuntu 14.04, there is currently no cinnamon packages in the Universe repository.

Via PPA for 11.10 and later

EDIT: 22/05/2014 - the PPA ppa:gwendal-lebihan-dev/cinnamon-stable has been removed or hidden from public view. I contacted the maintainer and the following is their reply:

The stable PPA is indeed no longer being maintained.

The nightly PPA is being kept for development purposes and should not be used on any sort of production machine (it can and will break at any time).

To be honest, I don't have an alternative to offer Ubuntu users at the moment, apart from switching to a distribution that does support Cinnamon. There are many such distributions out there, and I'm only hoping for someone to (finally) step up on Ubuntu's side to provide proper packages to its users.

EDIT: 25/04/14 - Two alternative PPA's have now been created - both claiming to enable the stable version of Cinnamon for Ubuntu users. I cannot vouch for the veracity of these PPAs

Option 1: 12.04 & 14.04 users only:

sudo add-apt-repository ppa:tsvetko.tsvetkov/cinnamon
sudo apt-get update
sudo apt-get install cinnamon

Option 2: 14.04 users only:

sudo add-apt-repository ppa:lestcape/cinnamon
sudo apt-get update
sudo apt-get install cinnamon

As an alternative you may wish to consider the unstable nightly automatic builds - please note Gwendal's warning above:

sudo add-apt-repository ppa:gwendal-lebihan-dev/cinnamon-nightly
sudo apt-get update
sudo apt-get install cinnamon

Option 3: In addition, you can also install cinnamon 2.2 in Ubuntu 14.04 LTS and derivatives by adding Linux Mint 17 Qiana repository in your system.

Open file /etc/apt/sources.list with nano command:

sudo nano /etc/apt/sources.list

Add the following line at the end of file /etc/apt/sources.list

deb http://packages.linuxmint.com/ qiana main upstream import

Update the repository then install the authentication key

sudo apt-get update
sudo apt-get install linuxmint-keyring

Update the repository again and install Cinnamon 2.2:

sudo apt-get update
sudo apt-get install cinnamon

After installation

Logout and select the Cinnamon session:

Enter you password and you'll see the Cinnamon desktop

... showing the traditional start type menu and applet design from Gnome-2

Extensions/Applets

The Cinnamon desktop uses the same philosophy as Gnome-Shell - functionality can be added to by installing Extensions & Applets.

Cinnamon uses its own Settings tool.

Cinnamon Settings

Cinnamon Applets

Similar to gnome-shell extensions - you can install applets from a dedicated Mint website.

I suppose you have Cinnamon installed and running in your computer.

Cinnamon has a Website with themes, extensions and applets. Here is the link for themes:

http://cinnamon-spices.linuxmint.com/themes

You have to download the theme you like and uncompress it in /home/your_user/.themes

If you do not have the .themes folder, you can create it. So you must finally have, for the Minty theme for example, the next path: /home/your_user/.themes/Minty

The Minty folder is the uncompressed theme. Into that folder there is another folder called cinnamon (check this for all the themes you want to install).

Then you will be able to select the theme you installed using Cinnamon Settings (program included with Cinnamon).

The GTK themes are needed for the windows. You can get them from Gnome-look.org, for example. These themes must be installed into the same path (/home/your_user/.themes). Then you can choose the GTK theme in Cinnamon using Cinnamon Settings too. You can't use Gnome-Shell themes with Cinnamon. You have to use Cinnamon themes.

Sorry for my poor english.

Ariel