Over the period of 2004-2006 one of my side projects was something called FlashGameMaker which eventually it ended up being called Buffoo. Right from the start of using Flash I liked the idea of creating a "Game Maker" a program which allow you to set a presets and out pops a game of your design, so that's what I set about designing. I eventually got it to the stage where you could make simple games, such as a space invaders clone (see images). It was a lot of work which unfortunately nothing came of, but it taught me some important lessons, the main one being always be away of simpler ways of achieving your goals.
Since then of course a large number of game making tools have sprung up (Unity, GameSalad etc) but I'm still interest in this area of game creation and will return to it one day.