Mathscribe Lite

Mathscribe Lite is a free dynamic graphing and mathematical modeling program. It solves and graphs equations involving standard functions found in algebra, trigonometry and precalculus classes. You can also use it to mathematically model scientific data, either by typing in the data from scratch, or simply pasting it from a spreadsheet or other program.

http://www.mathscribe.com/mathscribe_lite.htm