See also:

https://github.com/Orama-Interactive/Pixelorama

https://github.com/piskelapp/piskel

They're similar pixel art editor programs.

I always used MTPaint

https://mtpaint.sourceforge.net/

I guess it's a bit old but it works reasonably well, and supports a lot of different file formats which is occasionally useful.

I've also used GrafX2 for this kind of pixelart work. It takes cues from old Amiga paint programs

http://grafx2.chez.com/

Didn't know about Pixelorama, looks interesting.

Libresprite (since aseprite went evil) has been the only editor I can use for over a decade, glad there are others now.