The Python Numpy and Scipy libraries contain a huge number of maths and science related functions. Most of these are not directly available from Excel, but using the free ExcelPython package it is fairly easy to make the link, vastly increasing the functionality of Excel for maths, science and engineering applications.
I have collected interface functions to many of the (to me) most useful Scipy and Numpy functions in a Python module called xlScipy. These may be accessed from a free and open source spreadsheet: xlSciPy.zip.
The spreadsheet requires a copy of Python to be installed (including Numpy and Scipy), all other files, including ExcelPython, are included in the download package. Just unzip to a convenient folder, enable macros when you start up, and it should work. For those who have downloaded earlier versions of ExcelPython, this spreadsheet uses version 2.08, which is not compatible with earlier versions, so install in a different folder to the earlier versions.
The functions included in xlSciPy are listed on the first sheet (index):
There are ten functions for interpolation and fitting:
17 linear algebra functions:
12 functions for solving, creating and evaluating polynomials of any order:
All of the Scipy special functions (219 in all):
and 26 statistical functions:
Additional functions will be added as time permits.