In Plots you could do this in several ways - one way is to open the layout and plot to it. That would be something like
using Distributions, Plots
x, y = rand(Normal(), 300), rand(TDist(2), 300)
layout = @layout [a _
b{0.8w,0.8h} c]
default(fillcolor = :lightgrey, markercolor = :white, grid = false, legend = false)
plot(layout = layout, link = :both, size = (500, 500), margin = -10Plots.px)
scatter!(x,y, subplot = 2, framestyle = :box)
histogram!([x y], subplot = [1 3], orientation = [:v :h], framestyle = :none)
