Hudson has released a demo version of Puzzloop called Puzzloop Free [App Store].
Puzzloop is the original "match-three-of-a-king" circular puzzler released in 1998. The player controls a turrett in the middle of the screen that is surrounded by an inward-spiraling track on which a string of balls of varying colors close in on you. The objective: fire colored balls at the incoming string of balls in order to create groups of three or more that eliminate upon contact. Overall, we found the game to be fun and well executed (if you like this sort of game). Our full review also includes a gameplay video.
The free version is rather light and only contains a few levels, but if you are on the fence about purchasing the game, it may be able to help you decide. The full version of the game costs $7.99 [App Store].