SETL is a high-level programming language based on sets, especially mappings. GNU SETL is an implementation of that language, with some extensions.
Bleeding-edge builds can be made by cloning this repository and doing a "make" if you have Automake, Texinfo, and other tools of that ilk installed.
Otherwise, the path of least resistance is to grab a release bundle,
posted here as setl-X.Y.Z.tgz and mirrored at https://setl.org/setl/,
and unpack that. A "make" in the resulting setl-X.Y.Z dir,
in a POSIXish environment such as Linux or Cygwin, requires
a C compiler (usually gcc) and Yacc-compatible parser generator
(usually bison), but not the more exotic developer tools.
Please see also README.