A recent HN discussion about the Red language that is helpful if you don't know much about it: https://news.ycombinator.com/item?id=18843544
and I still don't get what's so special about it compared to the bunch of other embeddable languages (Lua, Tcl/Tk (which is 16MB in a batteries included package, mature, and shows why building a platform independent GUI into your language just doesn't age well)
However, GUI is not the main point of Red, just a part of it. IMO the really special thing is it's ability to create and use dialects (DSLs) very easily, so the 1 MB package can handle tasks from device drivers, through GUI, to natural language processing, with specialized dialects (DSLs).