Idle games are things where you let the game run, return after a while to do a some things, invest money or something similar. Thrones of Fantasy is really a good one.
You begin as a really weak guy who wants to become the best fighters. But you will have problem beating even a rabbit. So let the game run and wait until you have enough experience, some new equipment or spells. Then you will face something more difficult with the same fate, so let it go again. This way you can let the game go for hours and you will see small improvements. As an idle thing it’s really well-made.