Dungelot Tower of Fortune The Quest (not casual but awesome) Gamebook Adventure games RPG Quest Minimae Knight of Pen and Paper Star Traders RPG PixelSlime 1 (and 2) Pixel Defenders Puzzle Dungeon Village
Knights of Pen and Paper is creative and amusing but also grindy (which can be enjoyable). Yes... apparently it's now trendy to combine "casual" and RPG; nonsense I say (since that is an oxymoron).
I second Tower of Fortune, Kights of P&P, and Dungeon Village, and The Quest - but like undeadcow said, NOT casual but awesome! Also, if I may throw my two cents in, KoP&P is cool... but has this feeling of being built around bite sized play, which I'm guessing you after considering the title of your post