itch.io

Tried using this tool since it seemed convenient, got an error on the console. I'm on Aseprite v1.3.9.2:

"[Root Folders]\Aseprite\scripts\Fonts\Aseprite Font.lua:453: bad argument #1 to 'insert' (table expected, got nil)"

I can vouch for Aseprite, it's low probably the most low-impact thing I've used for pixel art short of MSPaint. It's not as hard to understand as you would think, but you will certainly want to explore the UI and learn its hotkeys. Libresprite is basically a Free Open-Source fork of an older version of Aseprite, but it does what it needs to do.

dustdfg brought up Pixelorama and I can also vouch for that program, it's just a bit heavier in performance and I've had issues from leaving it running in the background for a while. It's really close to Aseprite in features and UI: also it's free and you can run it in a browser if you just wanna try it out.