Torsten: I think both are not as powerful as Keyboard Maestro
They aren't. That is, Sikulix isn't, I installed Karabiner, but I don't think I ever used it. I mentioned Sikulix a couple of years ago on the old CT forum. It's fun, free, and cross-platform (I think). As far as I can remember, it works fine (a bit slow though), as long as you open a window of an app always at the same spot on your screen. Which I don't.
I think both are not as powerful as Keyboard Maestro, but maybe someone needs some more to to play with, e.g. Sikuli(X) with image recognition.
Karabiner - a powerful and stable keyboard customizer for macOS
Sikuli (or maybe SikuliX)