GNOME Do is not just an application launcher; with dozens of plugins, it allows you to play music, search the Internet, upload photos to Imageshack or Flickr, send and receive Tweets (Twitter updates) etc. This one reminds me a bit of the Ubiquity plugin in Firefox, but this is more powerful that that.
Installation is very easy. Go to the Applications menu and click on Add/Remove. Then search for Gnome Do. Once you find it, select it and click the Apply Changes button.
After the installation is complete you can open GNOME Do by going to Applications -> Accessories -> GNOME Do.
First thing you can do is to set the summon key (when you press this key, GNOME Do will pop up automtically). To do this go to the Keyboard menu and double-click on the Summon action. Then press the key or combination of keys you want to use. (In the screenshow below you can see that I use Alt+Space)
After that you can enable some of the plugins which would allow you to get the best out of GNOME Do. Click the Plugins menu and then select the plugins that you want to use with GNOME Do.
Here’s an example of how to send a tweet using GNOME Do. First make sure that the Twitter plugin is enabled from the Plugins menue. Then while on the destktop, press the summon key. When GNOME Do appears, type in your tweet and press TAB. Then type twitter (you don’t have to enter the whole word) and press enter. Your tweet will appear in Twitter within a few seconds.