Replicube

Here is an excerpt from Replicube's Steam description:

Replicube is an open-ended programming puzzle game/toy about writing code to replicate 3D voxel-based objects.

SOLVE PUZZLES

The main content of the game involves trying to match a reference object by working out code that will replicate it. There is no "right answer", if your code produces the same object, it's correct!

PLAY AROUND

You can always open the voxel tool in "free edit" mode and just play around, making whatever you want. In addition to the main 3D voxel editor, there is also a bonus 2D image editor for writing code to generate 2D images and GIF animations. You can even save your image creation as the background image in the "OS" interface of the game!

JOIN THE COMMUNITY

Every puzzle has 2 leaderboards, measuring source code size, and execution efficiency. Often optimizing for one will be at the expense of the other. If you enjoy trying to squeeze a bit more out of your code, the leaderboards are waiting!

There is also an in-game online forum where players can share their own voxel creations, and even challenge other players to try to recreate them, all presented in an old-school online forum wrapper.