threepenny-gui VS fltkhs-themes-demo

Maybe? https://github.com/HeinrichApfelmus/threepenny-gui

Not if you use my Threepenny-gui library. 😉

If you really want FRP, use Obelisk (based on Reflex-Dom. I will call just say "Obelisk" to refer to Obelisk's dependencies Reflex-Dom, Reflex,... too). I like the author of threepenny-gui and the library has the great advantages of not needing GHCJS (Obelisk does not need GHCJS either theoretically but I do not know how easy it currently is to make it work without) nor Nix. But the library was originally built as a non-FRP library and it has been lacking essential FRP combinators for a long time.

The threepenny-gui library is probably best if you just want a simple way to make GUIs. However, it doesn't really do desktop GUIs as such: it displays your GUI as a webpage running on localhost. However, it does work pretty well with Electron, which gives you a desktop application.

For this purpose, I normally use threepenny-gui, which can be used with Electron. (As it happens, that combination is what I’m using for my current Haskell program.)

If you want to make a simple desktop GUI, fltkhs — which binds to the FLTK library — is a good bet, as it's the easiest to install of all the Haskell desktop GUI libraries (even on Windows!). Unfortunately, the FLTK library doesn't create the prettiest GUIs in the world (e.g. see the GitHub page). If you care about such things, the author has also released the fltkhs-themes library, which provides a set of widgets with a much nicer style - see the GitHub page for a showcase.