Some kind of hint system
I've been going back to this game on and off for the last day or so, and oscillating between "not a good idea, it's really rewarding to get past a hard level with no help whatsoever" and "OH GOD YES".
I'd agree that the difficulty ramp is a bit uneven and in places random-seeming, though. The level tehjonbro screenshots above is a good example - the following few levels I found much easier. Possibly it's because the trick you need to use to get past that one stage hasn't been needed in previous stages (IIRC), while the following ones are more or less all "look at stage, work backwards from apple to work out where you'll need to have support, execute". I think a couple of them I finished on my first go, even, while the one capped above took me several tries, jotting notes on a bit of paper and then leaving and coming back later.
The stage with the horizontal row of lock blocks across the centre of the screen, the one made entirely of boxes and the one with the lock blocks scattered seemingly-at-random (but totally not at random!) in mid-air were all ingenious. I'm totally stuck on the one with the staircase, box at the top-right and apple at the top-left right now, reduced to trying various things and working out systematically why they won't work rather than actually having any kind of coherent plan. :/
I'd like to see a more-polished version with better graphics and a nicer menu, purely because I think that would motivate more people to play it, and this is a fantastic puzzler that more people should totally play even though it will make them feel bad about their puny brains for half an hour before giving them a tiny handful of happy success pills.
(I'd also like to see a version with a level select screen so I can go back and have another go at previous levels as I choose rather than having to start again from the beginning.)