Screenlets are small owner-drawn applications (written in Python) that can be described as “the virtual representation of things lying/standing around on your desk”. Sticknotes, clocks, rulers, … the possibilities are endless.
The goal of the Screenlets base-classes is to simplify the creation of fully themeable mini-apps that each solve basic desktop-work-related needs and generally improve the usability and eye-candy of the modern composited Linux-desktop.
The installation of Screenlets on Ubuntu Hardy/Intrepid/Jaunty /Karmic B4 (tested also in Karmic beta4)is easy, is just one command
sudo apt-get install screenlets
To open screenlets go to Applications—>Accessories—>Screenlets
You will got a Screenlets manager
You can use screenlets manager to start/ stop your screenlets
if you want to change the theme of a screenlets you will need to right click on the clock for example and choose the desired theme.
And is all, there are also other good softwares like screenlets like gDesklets, adesklets …
Links : http://screenlets.org/