Waste not, want not. This is a variant of Stockfish that only moves its cheapest piece(s) according to the standard valuation.

Here's a trivial endgame puzzle - Black to move.

Black has mate after 1...Rxa1+ 2. Qb1 Rxb1#, but let's see what Stingyfish thinks. Read the output here.

tl;dr—it played c4. Why use your rook when you still have a pawn?

Oops. White wins with Qf6#.

[github]

Modified from Stockfish and released under GNU GPL-3.0.