I put this engine (which is really still in the alpha stage of development) in the WinBoard beta package ( http://hgm.nubati.net/WinBoard-AA.zip ), as musky.exe in the Fairy-Max folder of that package. (WinBoard should be pre-configured to use it, unless you already used a previous version of that package, in which case your old settings would supercede the settings in the current package. In that case you would have to use the Load 1st Engine dialog to point WinBoard to the executable before you can use it.
After loading the engine you should be able to choose 'musketeer' from the New Variant dialog, after which it will show you a board from which you can pick a piece type, and then two gating squares, before it presents you with the start position from which you can play a move. You can also select 'Machine White' from the Mode menu to play the prelude from the black side, after which the engine will start to think. Gating will happen automatically when you move the piece that should perform it.

Screenshot of XBoard playing Musketeer Chess