Hop Drop (Free) by StormFrog is a matching puzzle game that has colorful balls dropping down from above and settling in empty cube spaces. When they find a place to rest, they become a block and are ready to be eliminated.
When you see three or more blocks of the same color adjacent to each other, give them a tap and you'll make them disappear. Any blocks that might be sitting above will momentarily turn back into balls, hop down, and again form blocks.
The aim is to keep going for as long as you can and accumulate the highest score. To help in your efforts, you are given bonus blocks and power-ups.
When you tap a bonus block, you will destroy all blocks of that color regardless of whether they are adjacent or not.
There are three objectives to meet at a time, which will allow you to unlock more useful power ups. For example: you must reach level six at least, match 15 cubes at once, and hit 2,500 points in a single game.
The first power up available is free and allows you to drag a bomb, from the bottom of the screen to destroy blocks in a radius around where you place it.
The balls fall down at a steady rate (until they speed up in later levels), which can start to feel too slow once you get used to playing. Fortunately, you can greatly speed up the ball's descent rate by giving your iPhone a gentle shake.
Hop Drop has clean graphics and soothing music. It does not offer enough challenge for hardcore puzzle enthusiasts, but is nevertheless fun to play, and the extra objectives serve to increase the replay value.