REDUCE is a freely available open-source interactive system for general algebraic computations, of interest to mathematicians, scientists, and engineers.
It can be used interactively for simple calculations, but also provides a flexible and expressive user programming language.
The development of the REDUCE computer algebra system was started in the 1960's by Anthony C. Hearn and further developed by Arthur C. Norman and others. Since then, many scientists from all over the world have contributed to its development.
REDUCE has a long and distinguished place in the history of computer algebra systems.
Other systems that address some of the same issues, but sometimes with rather different emphasis, are Axiom, Derive, Macsyma/Maxima, Maple, Mathematica, and MuPAD.
REDUCE is implemented in Standard Lisp. It primarily runs on either Portable Standard Lisp, which compiles to native machine code, or Codemist Standard Lisp, which compiles to optimized byte-code. It can also run on Visible Standard Lisp, an extremely minimal and highly portable Standard Lisp interpreter. PSL, CSL, and VSL are all included in the REDUCE distribution.
By modern standards, REDUCE is a surprisingly small and compact application, and runs well on all major platforms and operating systems ― including Android and iOS.