KnightCap is free software released under the GNU General Public License (GPL).
There is a fairly complex end-node evaluation process that considers similar features to other programs.
The most original feature of KnightCap, introduced in the late 1990s, was an experiment in temporal difference learning as applied to chess.
This technique allowed KnightCap to automatically tune the weights applied to the various features in its evaluation function based on the games it played.
For a while in the 1990s, KnightCap was quite active on chess servers on the Internet, but it is now semi-retired and rarely seen.