Houdini is a UCI chess engine developed by Belgian programmer Robert Houdart.
[1] According to Robert Houdart, Houdini's advantage against other top engines is in its handling of piece mobility, which is why it "favors aggressive play that tries to win the game".
Houdini 6 Pro supports up to 128 processor cores, 128 GB of RAM (hash) and is NUMA-aware, Houdini 5 Standard only supports up to 8 processor cores, 4 GB of hash and is not NUMA-aware.
Houdini 5 uses calibrated evaluations in which engine scores correlate directly with the win expectancy in the position.
On 20 July 2021, the Stockfish team announced legal action against ChessBase alleging that Houdini 6 and Fat Fritz 2 were in violation of the GNU General Public License.