Thank you very much!
Classied Encyclopedia of Chess Variants

Paradox! There are more engines than variants' players.
https://chessprogramming.wikispaces.com/Open+Source+Engines

Ha - ha! Demonstrate to me, please , test drive in the mountains! I know only one madcap: Mathias Rust, but he is a pilot.
I have one question personally to Mr. HGMuller. What (international) standard protocol (CECP) exists for variants' engines?
Of the popular protocols CECP (also known as XBoard or WinBoard protocol) is the one that has most support for general Chess variants. This because it defines commands that allow the engine to inform the GUI on game rules, such as how pieces of a certain type can move, what the initial board setup is, whether a piece that is moved should promote or make additional moves, etc. Other common protocols are usually dedicated to one particular variant. E.g. UCI (Chess), UCCI (Xiangqi) and USI (Shogi). These also assume a very limited function for the engine, assuming the GUI will do most of the work (e.g. they cannot be used for checking move legality, and cannot offer or accept draws, or resign).
The Classied Encyclopedia of Chess Variants D. B. Pritchard (2007) being a second edition of The Encyclopedia of Chess Variants is available online at http://jsbeasley.co.uk/encyc.htm - people may already know but I post it just for info.