Kalculator

Kalculator is a desktop widget that wraps up a basic calculator for the average user. It features support for basic mathematical functions, as well as for some trigonometric operations.
The widget runs on top of the Yahoo! Widget Engine, without which it cannot launch. Aside from this dependency, there are no other requirements.
In order to accommodate the program on your system, simply double-click it and give it permission to install, after which you can get acquainted with its minimalistic and user-friendly GUI.
By default, the widget is set to show the numerical view, which allows for a restricted set of operations such as additions, multiplications, subtractions and divisions.
If you’re looking for more advanced functions, press the button labeled ‘fun’, at which point you will be presented with a few trigonometric operators such as sin, cos, tan, asin, acos, atan, square root, logarithm, exponent and inverse functions (1/x).
The precision of the results is pretty satisfactory, of about thirteen decimals - quite alright compared to other calculators. What bothers though is the fact that you have to switch between the numerical and ‘fun’ views in order to input the numbers you want to operate in the latter.
A simple right-click on the widget reveals another set of features, amongst which the possibility to convert length, mass, volume, temperature, as well as to show the HEX representation of a given number.
As far as customizations are concerned, you are provided with a few built-in skins that can change the program’s appearance, as well as with options to tweak the opacity of the interface.
On an ending note, Kalculator is rather a basic application that cannot compete with a scientific number cruncher, because of its limited functionality. It appears that it won’t be receiving updates anymore, since Yahoo! Widget Engine itself has been closed down a while ago.