I see a neat GUI application that looks straight-outta-92, though the author describes it as "modern."
At this point, I read "modern" in an application's description as a subtle way of saying "not old and busted like all of the shitty competing projects."
Can run on Windows, Linux and macOS.
Open source, free, no need to install.
Just double-click, and then you can use it freely.
Before use, you only need to install gnupg.
Supports multiple languages.