Since you didn't explicitly mention Ruby, I would dare to suggest Lazarus, which is Free and open source, multi platform and produces compiled native code everywhere.

https://www.lazarus-ide.org/

That is the quickest and most straightforward way of making GUI applications I'm aware of, with the only drawback that it uses Object Pascal as supported language, but being it Open Source I can hope one day we'll see some support for other languages too.