SETL is a high-level programming language based on sets, especially mappings. GNU SETL is an implementation of that language, with some extensions.
This GitHub repository, which hosts development between GNU SETL releases, is based on a distribution at https://setl.org/setl/. That distribution archive is copied here as setl-X.Y.Z.tgz.
It is recommended to install GNU SETL from such an archive, rather than from a clone of this repo, unless you don't mind the loss of file timestamps that attends git clone (which causes unnecessary flutter with automake, needlessly repeated operations during builds, etc.).