Foxy Bricks is a very simple, very fast Lego instructions list. I built this for my son who loves getting instructions off the internet and building the sets with the legos he has, in between getting new sets, of course. My son is not old enough to read, so the app is extremely simple. A long list of every lego set, with pictures. Tapping a set gives you the instructions. Instructions that are tapped will be floated to the top of the list so you don't have to scroll through hundreds of sets to resume building.
Eventually I'll add filters, like Theme, Brick Count, etc. Especially if there is high demand for it.
I am not affiliated with Lego, I am just a fan.