Most merge puzzles drop pieces from the top of a box. Gravity Merge turns that around: the play area is a round pit, gravity pulls everything toward its center, and you release orbs from the outer rim. Because of that pull, each orb curves on the way in and lands where the physics takes it, not exactly where you aimed.
Two identical orbs that touch combine into the next size up, and there are eleven tiers in all, from a humble Pebble to a Supernova that shakes the whole screen. Move the mouse or slide a finger around the ring to choose a spot, then click or tap to let go. Quick chains of merges raise a combo multiplier.
The danger is the red ring: a single orb resting on it ends the game. Keeping the pile tight around the middle buys you space. Number fans will recognize the climbing-tiers idea from 2048 Classic, which plays it out on a flat grid.