This has existed for a long time from freedesktop.org, XDG specs, window manager extended hints, and so on. And it's gotten better too - did you know KDE3 had

This has existed for a long time from freedesktop.org, XDG specs, window manager extended hints, and so on. And it's gotten better too - did you know KDE3 had it's own sound mixer daemon? It was called ArtsD. Now we have pulseaudio, or whatever, which is great and cross desktop DBUS made it everywhere as well - I believe initially KDE3 as well did not have DBUS but had something called, DCOP. so - yeah things have improved a lot and many things - even command line tools 'playerctl' interop well based on this. More fun is also like libreoffice is compiled with many different file pickers, so on KDE you can use the native Qt extended KDE file picker, and on Gnome you get the GTK one.