CA 91104 Eval is an interactive floating point C-like expression evaluator. You give it an expression with numeric constants and variables and functions, and it churns out a numeric answer. You can use it to immediately evaluate an expression from the DOS prompt, or you can run it interactively, storing variables as you go so that you can do more involved calculations.
Documentation is built-in.
Eval's features include good precision, input and output in any number base, a large number of built-in functions and constants, flexible numeric output format, and ability to save and recall sessions from disk. The source code is included with this distribution. Look at the readme file from the program.