I read about it about a year ago. It was about a small program with 4 letters and someone posted 2 blog posts about it in a weeks time abusing the tool to see what it can come up with. The tool or program seemed to have an exploitative nature and seemed to be used in the security field. It worked with, I think binary files, but I recall it also allowed other programs to be ran on it. You provided an exit state and an input state and the program it needs to work with and tried all sorts of things within the provided program to reach the provided exit state. The blog post abused it to optimise to something interesting which I can't recall anymore. The writer of the blog post had more experience with it and already liked to toy around with it. It's not angr.

Iirc it 2as called something like nmap or jobn. Something with 4 letters and not the most straightforward name.

Please help me out.