A very simple tool that basically just takes Godot's OKHSL colour picker and makes it a standalone program. OKHSL is a version of HSL that normalises perceived brightness among hues, making it easier to pick colours that match in "real world" brightness. For more info, read here.
The interface for the colour picker is entirely built by the Godot devs, all I did was wrap it up in a nice standalone window with the ability to pin it, making it "always on top". You can check out Godot here, and view/contribute to its source here.