Google can be used as a calculator really handier than the Calculator application of Mac OS X.
RubyCalc may be what you are looking for. It supplies an application with its service, and a widget.Caution : RubyCalc is using the Ruby language to perform computations. This language has some specificities, like integer divisions, pow operator, modulo operator (for instance). Be sure to understand theses specificities by reading the documentation, otherwise you may not understand the result. Examples : 5/2 = 2 (integer division) 5%2 = 1 (modul) 5/2.0 = 2.5 5^2=7 (binary exclusive or) 5**2 = 25 (pow)