GraphCalc is a very handy programmable graphing calculator and it's open source! Development seems to have stopped in November 2003 but since the source code is hosted at SourceForge I expect to be using it for many years to come.
The calculator I use the most is Calc98 from Flow Simulation Ltd. There is a free version but, I liked it so much that I bought the commercial version. I use it on my desktop PC's and my Jornada 720 handheld. Many other Windows hardware platforms are also supported.
When I need to work with complex equations I often use MathCAD by Math Soft. It also makes documenting and publishing the equations easier. I currently run version 11 and have used prior versions for over a decade. The only thing I don't like about v11 versus previous versions is the usage of Macrovision copy protection. I hate having to run a Windows service to keep me honest.
Last Updated 09/04/2010