wtf is sunsetter7?

Sunsetter is a chess engine, a program that plays chess. This particular version has been adapted to work with lichess.org, a popular free online chess platform. It's based on an older open-source chess engine originally hosted on SourceForge, updated here to integrate with lichess's systems. The README doesn't go into much detail about how the engine actually works under the hood. What we can gather is that it's written in C++ and runs on Linux, Mac OS, and Windows. There's a reference to a related project called "fishnet," which is lichess's distributed network of chess engines that power bots and analysis on the platform, so this version of Sunsetter was likely patched to be compatible with that ecosystem. This project would be relevant to people involved in running or contributing to lichess's infrastructure, the maintainers who manage the pool of chess engines that players can face or use for analysis. If you're a developer interested in how chess engines get integrated into a platform like lichess, or if you want to build on or study an open-source chess engine, this is the kind of codebase you'd look at. Not much else is documented in the README beyond build status badges and the fact that it's released under the GNU General Public License v2, meaning the source code is freely available and can be modified and redistributed under those terms. If you need deeper technical context, you'd likely need to look at the fishnet project or the original Sunsetter source for more background.