Mahjongg Titans is a solitaire game which comes free with Windows Vista. In this classic Chinese tile game, you remove matching tiles two at a time only if they can slide left or right freely, with nothing on top of them.
So in the above image, on the far right center is a 7 of dots which can slide right. On the lower row is also a 7 of dots which can slide right. By clicking on one of those tiles, and then the second, both get removed from the board. The aim is to clear the entire board with this tile matching activity.
There are "levels" to this board. That is, some tiles are stacked on top of other tiles. In the very center of the board for example is a N - a North Wind. It is on top of another North Wind tile. You cannot remove the lower North Wind tile until that upper one is gone. There is another North Wind tile visible on the board - in the upper right corner. However, it is currently blocked by a red dragon. There are no other red dragons visible on the board yet - they must all be hidden down below other tiles in the center. So those tiles are all in essence "stuck" until we make some progress.
The layers of the board can be a bit tricky to see until you get the hang of the game. For example, in the second row up from the bottom, all tiles from the 4 of bamboo on the left to the 1 of bamboo (the tile that just looks like a tall green bamboo plant) are on a "second level". There are tiles down below those. On the third row up from the bottom, the pair of 7 tiles with kanji on either side are both on that "second level". However, the tiles from the 7 of bamboo on the left to the 3 of kanji on the right are now on the "third level". It is like they are stacked in an every ascending tower as they get towards the center.
The real key here is that you cannot know what is hidden in that tower until you start moving away tiles. You do not want to end up in a situation where a tile is on top of its matching tile, because that would cause an unwinnable game. You want to always try to clear tiles where you know where all four of them are, to know you aren't trapping a tile. Of course sometimes that's not possible, but that is your goal.
Well recommended as a great logic puzzle game with a beautiful set of tiles! Note that the set I show in my screenshot is just one of many tile sets and backgrounds you can choose from.
NOTE: I do not think you can buy this game separately. It comes free with Vista, so if you're interested in this game, it might be time to upgrade to Vista!