The REDUCE computer algebra system is released free-of-charge under a modified BSD license. It can be obtained in various versions from SourceForge. Instructions on downloading it are available here.

REDUCE is based on a subset of Lisp called Standard Lisp. In order to help users choose the best version of REDUCE for their purposes, we describe the general characteristics of the relevant Lisps.

The available  versions of REDUCE are based on two different Lisps, namely:

1. Portable Standard Lisp (PSL). This is currently the Lisp used most widely for running REDUCE. It evolved from the original Standard Lisp definition, but now contains many more facilities. It is quite efficient in its use of both space and time, and has been optimized for algebraic computation. All PSL versions of REDUCE are distributed with sufficient PSL support to run on the given computing system. PSL is supported on many architectures and is an ideal system for those wanting to run REDUCE as a standalone system. The current principal developer of PSL is the Konrad Zuse Center, Berlin (ZIB).
2. Codemist Standard Lisp (CSL). This is a Lisp system written completely in ANSI C, which makes it very easy to port to a new machine. Like PSL, it is a faithful implementation of Standard Lisp and has been optimized for running REDUCE. It requires a very small memory partition for its Lisp support. Furthermore, most of the REDUCE facilities are supported as machine independent pseudocode, which is quite compact. In the worst case, the performance of this system is about a factor of two slower than PSL, though in many cases it matches PSL performance. However, the memory use is smaller. All CSL versions are distributed with sufficient CSL support to run on the given computing system. This is an ideal system for those wishing to embed algebraic calculations in a C-based programming environment. The developer of CSL is Codemist Ltd.