The 5-free calculator is the good article.

**SFR Calc**

SFR Calculator has an MS Office-like interface. It also gives you a choice of three skins. Unlike other free calculators, its use is similar to the kind we do on paper. You can use it like a text editor and add comments or any other annotations to your calculations. The advantage of the tape style of calculations is that the calculations can be kept as records and even printed out. The calculator may not be suitable for power users but can be used to perform accounting operations.
SFR Calculator (ver.4.0.6) is an 8.6MB free calculator download. It is supported on Windows 2000, XP, 2003, Vista, and Windows 7. Versions of SFR Calculator are available for Windows Mobile and the iPhone.

**Speed Crunch**

SpeedCrunch comes as an installer and also in a portable version. It has a clean user interface and a very intuitive response to your inputs. SpeedCrunch calculates even as you type and this auto-completion behavior is quite handy when it comes to result speed. Results are precise up to 50 decimal points. Syntax highlighting also minimizes errors as you type. You can feed in formulas, constants, and functions from the extensive library that’s available. SpeedCrunch supports unlimited range of alpha-numeric variables and it also lets you store your own for later use. If the stored variables are too many, there’s a handy search bar to help locate them.

SpeedCrunch records everything in history and you can easily recall and reuse a previous expression. You can also save a session for later use.

SpeedCrunch (ver. 0.10.1) is a 2.4MB download. It is supported on Windows, Mac OS X, and Linux.

**Space Time**

SpaceTime goes beyond the idea of just a free calculator and falls into the category of an advanced scientific application for power users. There are interactive tutorials which help you to start off with the app. SpaceTime has support for 2D and 3D graphing features. The scientific calculator has a large catalog of functions. The mathematical software covers algebra, computer algebra system (CAS), trigonometry, statistics (scatter plots, probability plots, histograms etc), and calculus among other capabilities. You can also enter your own scripts for solving loops, recursion and generating functions. Ultimately, you can capture screens, frames and results with a click.

SpaceTime (ver.4.0) is a 1MB download. It is supported on Windows (2000, XP, Vista, and 7) and Mac OS X. SpaceTime can also be downloaded for the iPhone and the iPad (not free). SpaceTime requires an obligatory free registration for use.

**SpeQ**

SpeQ is a mathematical software which uses a sheet (or tape) just like the two we have mentioned before. But unlike them, SpeQ offers a library of computational functions. You can define your own variables and use them in your functions. The software has 100 pre-loaded constants plus 130 built-in units. You can plot graphs and trace the plotted functions. The memory list helps to reuse all previously defined functions and variables. You can add in your comments in the sheet, save it, and also print it out.

SpeQ (ver.3.4) is a 520 KB portable download. Installer is also available. It is supported on Windows (all).

Scientific Precision is available for trial base and not a free one.

A handy, fast, reliable, precise tool if you need to perform complex mathematical calculations. Scientific Calculator Precision 90 is programmed in C#. All calculations are done in proprietary data type. The calculator handles mathematical formulas of any length and complexity. Calculation history can be stored into text file or printed. There are ten variables or constants available for storing often used numbers. Prebuilt Common Costants list with fundamental constants. Unlimited User Constants list. Precision of calculations is 90 digits. Trigonometric, hyperbolic, inverse and combinatorial functions. Special numbers NaN, Uncertainty, and Infinity. The calculator follows classical approach when uncertainty of f(x) calculation is estimated by formula max|(derivative(f))|*|x*uncertainty(x)|, where maximum of function derivative is considered on interval [x-uncertainty(x),|x+uncertainty(x)], and uncertainty(x)=|x|*10^(-precision). Gamma function, Lower Incomplete Gamma function, Upper Incomplete Gamma function, Beta function, Incomplete Beta Function, Sine integral function. Summation and product operator have four levels of nesting.