FreeCalc is a great replacement for your existing Windows calculator. it is the standard Windows calculator but with much more options.

Excalibur is a freeware full-featured RPN-only calculator with 300 functions (scientific, business, conversion, computer science, physics, complex numbers, geometry, vectors, etc), full 4 or 8-level stack, international support for different comma and decimal point formats, programmable, macros, registers, custom button banks, etc. It's difficult to find a freeware calculator so powerful!

Version 5.6 available, A powerful scientific calculator with statistics and financial functions, but it doesn't take up very much screen space

ESBCalc is a Scientific Calculator for Windows with Infix Notation, Brackets, Scientific Functions (Trigonometric, Hyperbolic, Logarithmic) plus more.

AB-Euro is the Free Currency Calculator for your desktop. You may convert between all Euro-based and 35 foreign currencies.

RF21 for Windows is a scientific calculator, plotter, programming and numeric system in one. It allows for permanent installation of a user's own commented functions and libraries. Such user functions may have one or several arguments and values. Works as an archive at the same time, with integrated searchable database, to let you find and reuse materials created years ago. Each function self-reassembles when its name is called, autonomously searching the libraries for all components needed. Predefined functions include gamma, zeta, psi and Bessel functions, error integral, cumulative Binomial distribution and more. On top of these and the

CyberCalc is much more than a calculator. it calculates (area, length, weight, volume, temperature, time, speed, pressure and energy)

pmaCalc combines a scientific calculator, binary arithmetik for programmers, and unit converter in an interesting package.

SkinCalc is a free skinnable calculator with more than 100 different skins available for download.

EuroCalc is a free calculator and currency converter, Stays on top option, Copy and Paste functions, Decimals place adjustement, Knows Euroland currencies.