Secrets of the Castle Match 3

Swap gems until three of the same color line up — that's the whole engine, and this one doesn't try to reinvent it. What it adds is a castle setting and a long run of levels, with locked tiles and blockers showing up more often the deeper you go. It's the kind of game you can play in five-minute chunks without losing your place, since a failed level just resets clean rather than costing you progress.