[lispm]

The best GUI support for Common Lisp one gets from the commercial implementations Allegro CL and LispWorks. Both have cross-platform GUI libraries (ACL for Windows and Gtk, LispWorks for Windows, Gtk, macOS and Motif). Both have their IDE implemented with their respective GUI library. If one would wants to write a substantial GUI application in Common Lisp, that's one of the reasons people pay quite a bit money for those implementations and for commercial support.

There have been very substantial GUI applications implemented with both systems.