Yacas is an easy to use, general purpose Computer Algebra System, a program for symbolic manipulation of mathematical expressions. It uses its own programming language designed for symbolic as well as arbitrary-precision numerical computations. The system has a library of scripts that implement many of the symbolic algebra operations; new algorithms can be easily added to the library.
Mawk (Mike's AWK) is an interpreter for the AWK Programming Language.
Saxon is a XSLT 3.0, XQuery 3.0 and Xpath 3.0 processor for Java.