GRFON (General Recursive Format Object Notation) is a human-readable serialization format, similar in purpose to the older JSON and XML formats. GRFON (pronounced "griffon"), however, is designed to be easier for humans to read and write, using any simple text editor.
GRFON was introduced in 2015 with this blog post. It's one of the serialization formats (along with JSON) supported out-of-the-box with MiniScript and Mini Micro, and is starting to catch on in other contexts too.
See the documentation for more about GRFON syntax, or jump right into the examples.