There are probably many more, but these are the ones that I could find after a quick research. Editors like Overlap2D, Mundus, Hyperlap2D, ... don't count because they have a UI and aren't pure code.
Edit
I understand that some of these aren't making things useful or easy but still, they may be helpful to somebody!
Adding LibGDX is probably worth doing because many beginners might stumble upon them and ease their journey.
I'm talking about frameworks that extend or simplify the usage of LibGDX.
Here are some of my suggestions:
There are probably many more, but these are the ones that I could find after a quick research. Editors like Overlap2D, Mundus, Hyperlap2D, ... don't count because they have a UI and aren't pure code.
Edit
I understand that some of these aren't making things useful or easy but still, they may be helpful to somebody!