If you have five spare minutes, Ocean Plus Pairs will fill them. Everything happens on one screen with a 6×6 grid with 18 pairs, and the whole thing runs straight in the browser - no downloads, no sign-ups, no fuss.
Two cards flip per move; match them and they stay open, miss and they flip back after a beat. The whole skill is building a mental map of what you have seen without losing your place. With a 6×6 grid with 18 pairs, later flips are genuinely tense - you know the pair is out there somewhere.
The loop is deliberately compact: one round takes minutes, improvement is visible, and the next run is one tap away. That makes it a reliable filler for short breaks - and an easy game to recommend to someone who 'does not really play games'.