Betwarrior
Betwarrior is a small, sharp battle of pure position. The board starts completely packed with alternating stones - no empty squares, no setup phase. On your turn you take one of your orange stones and slide it onto an orthogonally adjacent slate stone, clobbering it off the board. That is the entire rulebook: one step, always onto an enemy, never onto empty ground.
The catch is what capturing does to your own mobility. Every clobber changes the shape of the board, opening lanes for you and closing them for your opponent - or the reverse, if you are careless. The side that runs out of legal moves on its turn loses outright, so the real skill is reading two or three moves ahead and steering the position toward a shape where you still have options and your opponent does not.
You play White against a computer opponent that plays Black with a genuine search: it looks ahead by minimax with alpha-beta pruning, weighing mobility and material, and it never makes an illegal move. Twenty levels raise the stakes by growing the board and deepening the AI's lookahead, from a compact five-by-six opening skirmish to a wide seven-by-eight campaign against an opponent that plans several moves out.
No timers punish thinking, no purchases buy an advantage - every star and every coin is earned by outplaying the machine on the board in front of you.
Betwarrior - tap, adjacent, capture, win