Open source engine / software for makruk?
The only open-source makruk engines I know of are:


fairymax
Sjaak II
Stockfish


The latter is my attempt of adapting Stockfish for makruk. Below you can find some recent test results. I can not give an estimate of how these engines compare to strong human players though.

Rank Name                          Elo     +/-   Games   Score   Draws 
1    stockfish-mak-f364111         359     103      80   88.8%   15.0%    
2    Bilis_v1.0                    127      65      80   67.5%   32.5%    
3    sjaakii-1.4.1                 -61      60      80   41.2%   40.0%    
4    fairymax-5.0b                -174      62      80   26.9%   38.8%    
5    NebiyuAlien                  -185      55      80   25.6%   46.2%