Gpg4KDE was a project by the German "Bundesamt für Sicherheit in der Informationstechnik" (BSI) to integrate GnuPG with the Software KMail (Kontact) for GNU/Linux systems. This was done at the beginning of the century as back then there was no groupware client with GnuPG support on Linux. The changes found their way into the mainline of the respective projects so when you install KMail, Kleopatra and Dolphin on Linux you will have full integration with GnuPG in these User Interfaces.
Since 2022 the authors of GnuPG additionally provide an AppImage with Kleopatra and GnuPG equivalent to the latest Gpg4win release. See: https://gnupg.org/download