Cool game!, Pretty original to me.
I didn't need the tutorial to do it so it has potentail to make a good textless tutorial, maybe if you could communicate to the player that you can use the right click in order  to go between worlds and more basic levels in order to introduce the mechanics, like just one level to tell the player that this cube can interact with buttons and the other cannot. But other than that and if you decide to further develop the game, a bit of polishing here and there like the players movement and the graphics could make the game even better.  Pretty good game.

Nice relaxing puzzle ^^ the box sometimes falls back to the other side but the idea is good ^^

This has real potential. But it needs a better tutorial and difficulty curve. Easier levels. My real criticism is that it's probably too ambitious for a jam. I respect the attempt a lot though! 

The audio was pretty nice! Gameplay was fun, but a bit confusing at the start. I can definitely see how more complex puzzles can be made with this concept. The spheres around the buttons looked really cool!

A bit confusing at first, but when you get a hang of the controls and mechanics, it's a pretty fun entry for the jam overall.

As a reference to future players, since nobody seems to check game descriptions during jams:

 -You can swap between the 2 worlds with right mouse button or left alt

 -You complete a level by standing on red circles in both worlds

 -Buttons with white borders can be activated by the player, and black borders by cubes

 -Blue circles teleport cubes between the two worlds

Got nice Portal vibes! I found pretty hard to understand what the goal is. The grabbing of the black cube is a bit unreliable too. But really cool idea for the two worlds! Could lead to nice puzzles!