Windows lightweight Math Software I'm looking for lightweight, free, Windows, Math software.
Something I can put an expression and get an answer, or graph it.
I tried Euler, but it is quiet complicated and HUGE.
Basic needs:


*

*Expression Based

*Supports Variables

*Support Functions, User defined and auto loaded.

*Supports graphs, 2D.  Not really needing 3D.

*Supports History.


What do you use?  What do you recommend?
 A: As calculator wxMaxima (screenshots) with export to png and LaTeX syntax.
For playing with graphs I use GeoGebra with export to png, eps, pdf...
For some special cases Wolfram|Alpha.
And also MS Excel.
And also a normal calculator - is often faster than PC programs ;)
A: I'm also interested in answers to this questions!
There is a Power Calculator from MS, but has a lot to be desired.
A: I haven't personally used CPMP-Tools, but I've heard it referred to as a free CAS.
A: Graphmatica does a fairly decent job at plotting functions. Not very powerful, but it can graph a lot of functions and their derivatives and such.
A: In your position, I'd just use an interactive Python shell with Matplotlib. (But then, I'm a computer science guy first and foremost.)
A: I have also found SpeQ Mathematics.
It is very lightweight, starts quickly and has some good functions.
A: You can try PARI/GP
I am more fan of sage but currently it doesn't natively support your OS, you can try it in a virtual machine.
A: I'm not sure if it supports user defined functions but I've found Microsoft Mathematics to be extremely useful.
A: Also, try DMelt program for scientific computations. It is 100% Java, runs on windows and free.
jPort also runs on Windows (Java) and can install about 10 free math programs that run on Windows.
A: Also, try GAP, an open-source system for discrete computational algebra.
To install in on Windows, I recommend to use the .exe installer downloadable from this link which always points to the latest official GAP release.
Documentation on GAP is included in the distribution and is also available online. In particular, see the GAP Tutorial and GAP Programming Language.
A: You may consider TeXmacs, it is a free wysiwyw editing platform with special features for scientists. 
More related to your question, you can interface it with a lot of third party mathematics tools for algebraic calculus, graphing, numeric calculus, etc.  

Developed on GNU/Linux, it runs under Windows and Mac OS X as well. I guess the best user experience is with GNU/Linux.
Downside of TeXmacs regarding your question, it is not exactly lightweight, although absolutely free software.
