UIs and networks for Julia.
(If you really wanted to have lots of control and a proper web framework, you could use the web framework Genie.jl.)
I can plug into classic C++ immediate mode Dear Imgui via CImGui.jl.
Reactive.jl is widely used to manage signals in UI toolkits. It has a competitor Signals.jl, whose creator describes the differences:
Signals.jl, while offering the same functionality as Reactive, is different on some key factors
Dynamic: Signals are not typed, you can push an integer then float64 and then a string and it blends nicely with Julia’s Multiple Dispatch
Push-Pull: you can either push a value into a Signal and propagate changes along the Signal graph , or you can set a value without any propagation and only pull the necessary changes from any other signal.
Syntax: Syntax is somewhat simplified, square brackets to set or query a value, round brackets to pull or push a value (see documentation for more examples)
The last point is, IMO, a minus, but the second one is a plus.
Traditional UI toolkits
QML.jl magically plugs into Qt5. Gtk.jl plugs into GTK.