Stockfish is a good one. Though the original codebase was called glaurung or something like that. Written mostly by one person or a small handful(the original a

Stockfish is a good one. Though the original codebase was called glaurung or something like that. Written mostly by one person or a small handful(the original anyway), I think. Obviously successful, wildly influential in its niche, and the code is open source. Though honestly if you were gonna read a chess engine, might as well read modern Stockfish. You'll learn a lot about squeezing out every last cpu cycle and byte of memory, as well as parallelism in a non- "embarassingly parallel" problem domain. I recommend starting with the transposition table(ttable.cpp), since it's very self-contained. GNU Emacs also comes to mind I suppose.