Noticed this in my distro’s repo today (fedora) and figured I’d bring some attention to it. Asesprite is the premier pixel art tool, so it’s awesome to see someone keeping the FOSS version alive!
There’s also a great book from NoStarchPress made for Asesprite, and assumes absolutely no previous artistic knowledge!
FreeCAD is probably what you’re looking for, it had a bad UI but just released 1.0 recently and is pretty decent now. Also I really recommend checking Pixelorama over libresprite for a FOSS pixel art tool.
I’d heard of pixelorama a few years ago when it was released, but looking at it now, it looks like it’s come a long way, very impressive.