MiniCalc GUI is a calculator that supports user-defined functions and graphing.
It starts instantly and runs on both Windows and Linux.
It is easy to use for the average user, but also supports factorials, exponents, logs, and trig functions.
Quicksolve is an interactive graphing calculator and programming language. It provides an intuitive interface for performing basic plots and calculations with a focus on numerical solutions. Versions will be available for both Gnome and Mac OS X.
C# Website system. This is going to be the "Newer" Internet, and even has a custom theme system. This is going to let users do "anything" that won't harm the client computer in any way.