Max
From Just Solve the File Format Problem
Max is a commercial visual programming language produced by Cycling 74. It is a data-flow programming language that uses "objects" connected by wires. In the tradition of modular synthesizers, Max files are often known as "patches."
Identifying Max patch files
The extensions are .max (up to Max 4) and .maxpat (up to Max 5). Max 5 patches are not backward compatible.
.maxpat files are plain-text JSON files. There doesn't seem to be any documentation for .maxpat files, but they are more or less readable.