The world is full of Mahjong solitaire apps. I've played my share of those too, but I get bored. I love Mahjong, the traditional game for four. My uncle had a proper Mahjong (well, probably still does) and we used to play it when I was a teenager.
Yesterday I was flipping through pages of iPad apps, just scanning the iTunes store, and decided to search for Mahjong apps, hoping to find a non-solitaire version. And I did! Actually, there seem to be several of them, but they are buried under the masses of solitaire ones.
The one I downloaded first was Mahjong Time Lite which is a free one. I started playing and after a half an hour it told me to take a short break and continue playing in a couple minutes. The Mahjong Time Lite free version is fully functional, but has a time limit of 30 minutes. The "layover" in between sessions isn't long, but I don't know if it continues the preivious game or not after the break - I didn't wait to see, but downloaded the paid version for 1,59€ ;)
After some googling I noticed that the Four Winds Mahjong seems to be a bit more sophisticated still, and apparently the more popular traditional Mahjong, but I know myself: I will play Mahjong intensely for a week or two, then I'll more or less forget about it and maybe get back to it only occasionally. And for that behavior pattern $5,99 (5,something in euros) is a bit too much. So I'll go with the Mahjong Time :)