Every chess piece is, mathematically, just a list of moves — offsets from where it stands. A Knight is eight L-shaped jumps; a Rook is “slide along a rank or file until something stops you.”
On Super Chess 16x16 you edit that list yourself. Open Settings → Program the chess game, pick a piece and a move type (jump to leap, slide to travel until blocked, or step for an exact offset), then click squares on the board to add moves. Right-click a move to remove it. Save, and that piece now moves the way you designed it.
Because both players program their own rosters, balance comes from the matchup, not from the pieces being equal. The skill is designing a roster that is more useful than your opponent's.