I just released Fairy-Max 5.0a, which as a main improvement over previous versions has that it can now handle boards of other than 8 ranks deep. This has been used to add seven new variants, on 6x6, 10x10, 11x10 and 12x12 boards. Other features that had to be added to make these variants possible were initial Pawn triple-pushing, and the associated e.p. capture on both squares these skip, double-pushes of a Pawn that already made a single step, castlings where the King steps 4 squares towards the Rook, interpreting stalemate as a win, Pawns starting on other ranks than the 2nd, and promotion to the piece that started on the promotion square. All that can now be configured in other variants as well.
In addition it now supports analysis mode with move exclusion, and a persistent hash table, in any variant.
For more details, see http://www.talkchess.com/forum/viewtopic.php?t=59059 .