Tools

Collaborative drawing

Excalidraw (source) : an online whiteboard.

Drawpile (source) : a desktop software, real drawing one, compatible with the ORA standard.

Pixel art

LibreSprite (source): pixel art drawing application.

Pixelorama (source): pixel art drawing Godot based application.

Voxel

Goxel: Open Source multi-plateform voxel editor.

SVG

InkScape: SVG editor.

GodSVG: SVG editor Godot based application.