In the past we have introduced you to FreeCalc a free alternative for Windows Calculator which had some nice features built in, but we were completely bowled over when we came across SpeedCrunch a light weight, fast and high precision calculator for Windows, Linux and Max OS X.
SpeedCrunch is quite unlike a regular calculator, since it allows you to type expressions along with providing you with regular calculator features, so for instance if you want to add up two numbers you can type in sum(10+10) or if you are looking to get a square root of 16, you can use the expression sqrt(16). You can use several such expressions by using the built-in functions.
One of the most interesting features in SpeedCrunch is the ability to use variables for calculations, so for instance you can store a variable which holds the base rate of interest for all loans (you can add a variable by typing in br=9.5% and hitting enter), so the next time you want to find out the interest you will pay, simply type in 657*br, if the interest rate changes you can update the value by typing in the value again.
There is also a default variable called ans which holds the answer to the last calculation you did.
SpeedCrunch has several interesting features which include saving the calculations you do in a session, intelligent automatic completion where you are shown with functions that match what you type, history and results display in a scroll, auto corrections for common mistakes among others.
Overall this is a must have utility and goes in to the Techie Buzz Hall of Fame for applications.