Which open source chess engine has the most positional understanding? Most open source chess engines with hand-tuned evaluations are known for their innovations on search (Fruit, Stockfish).
I was inspired by HIARCS' generally more human-like play and the fact that neural network based engines like Leela suggest that we have more work to do when it comes to evaluation functions.
The reason is that I'd like to apply the same evaluation functions in a chess engine that I'm working on.
Which open source engines are out there are known for its deep positional understanding? Unfortunately, engines known for their positional understanding such as Shredder, HIARCS, and Komodo are closed source.
A really strong and great positional open source engine I have used is Rodent.  The last version was Rodent IV and is available at http://www.pkoziol.cal24.pl/rodent/rodent.htm
Of course Chess Programming wiki continues to be a good place to research and discover engines and the following link shows only open source engines.
https://www.chessprogramming.org/Category:Open_Source