Turnabout is an puzzle game developed by Artdink and published by Natsume. It was released in 2003 for the Sony PlayStation.
Turnabout consists of 100 levels, but the player can only access them in groups of ten, requiring most of the levels to be completed to reach the next ten. The game's main feature is the ability to rotate the stage 90 degrees in either direction (but not 180), causing all the dynamic elements to fall in that direction. The stages are grids, being about 16x16 at maximum size. The goal is to get all the colored pieces to disappear. There are colored balls, which are dynamic, and colored blocks, which are stationary and often act as blockages. When one ball (let's say red) collides with another (red) ball (or a red block, or many other red balls, etc), all of the (red) pieces that just touched now disappear. This repeats until the player is stuck (losing) or the player makes all colored pieces disappear (clear).
Although this may seem easy, the levels introduce a number of obstacles. Colorless blocks are dynamic pieces, which, unlike balls, are not limited to taking up only one space. Colorless blocks may have very complicated and specific shapes that make progression difficult. Colorless blocks can also not be matched, meaning they exist for the entire round. Balls and colored blocks can have five different colors (red, blue, yellow, green, purple). Each color can only match with itself, and can touch a block of a different color without disappearing. Speaking of colors, one of the more elaborate gimmicks of Turnabout is the 1 red ball 2 red blocks situation. In order to clear the level, all the red must be cleared. However, if we match one ball with one block, then the other block will still remain, requiring the level to be restarted. The solution is to get the ball to touch both the blocks simultaneously, matching all 3 at once. There are also other situations, including 2 red balls 1 red block, where the player must match all 3 at once while keeping the red balls separated at all times.
This game does include a level editor, where you can save a certain number of levels on your memory card and play them anytime. You will be limited to 9 colorless blocks, however.
Source: Wikipedia, "Turnabout (video game)", available under the CC-BY-SA License.