It includes three modules:
1) Scientific
2) Unit Converter
3) Quadratic Solver.

You can create your own modules using Microsoft's free eVC++ compiler.
Source code for the modules is included with the download.

SOURCE

http://www.handango.com/PlatformProductDetail.jsp?siteId=...

Reviews:

***** [Feb 25, 2005] by GMS using iPAC 3950
Three years ago I tried various RPN caclulators, CalcNow was by far the best. Had to repair my iPAC this year and it took 3 days and a few RPN calculator installs before finding CalcNow again!

***** [Feb 20, 2004] by Rick Harriman using Dell m60
Best RPN or regular calculator I have seen or used, nice interface, just very nice.