IUP is a cross-platform GUI toolkit actively developed at the PUC university of Rio de Janeiro, Brazil. It uses native controls: the Windows API for Windows, Gtk3 for GNU/Linux. At the time of writing, it has a Cocoa port in the works (as well as iOS, Android and WASM ones). A particularity of IUP is its small API.The Lisp bindings are lispnik/iup. They are nicely done in that they are automatically generated from the C sources.
