Wessa Mathematical statistics and forecasting calculators including an equation plotter, multiple regression modeling, and a variety of descriptive statistics from variability and concentration to percentiles and correlation. 
Mega Converter 2 Discover how many seconds old you are, the difference between a gallon in the USA and a gallon in the UK, how many nanometers in an inch, how many quarts in a chaldron and more. Handy scientific calculator is also available. 
Date Calculator Tells the number of days between two dates, or defines a date based on the number of days from a specified day.http://cgi.cs.duke.edu/~des/datecalc/datecalc.cgi  site info 

Calculator Tab Scientific calculator with features including long term memory storage, ambiguous input filter, possibility of switching between comma and point as decimal separators, and saving of settings between sessions. 
AKiTi Math solving resources for quadratic, cubic and quartic equations, along with utilities for rootfinding, maxima/minima of functions, N equations in N unknowns, numerical integration, data fitting and eigenvalues and eigenvectors. 
HIOX India Free PHP and Javascripts, background images, icons, clipart; HTML, CSS and PHP tutorials, link popularity checker, broken link analyser, calculators, converters, web directories and licensed scripts for commercial purposes. 
PHPSimplex A free tool which enables users to solve linear programming problems. The tool has no limits on the number of decision variables and no restrictions on the amount of problems. 
 