ProVerif is Free Software distributed under GPLv2.
Install with OPAM
opam install proverif
There might also be a dedicated package for proverif in your package manager. If you want to instead install it manually, consult the README and download:
More options on how to install ProVerif can be found in the manual.
ProVerif has first-class editor support in VSCode with a language server. Install the ProVerif Language Server.
Further, there is