They have little in common. Gadfly is for statistical graphs, roughly in the style of ggplot. Makie is general purpose, roughly in the style of matplotlib, but (I believe) better designed, way faster (after excruciatingly slow compile), much easier to extend with custom functionality, and awesomely interactive. There is a ggplot/Gadfly-like library built on top of Makie called AlgebraOfGraphics (homage to GGplot).