See Binary Factory: "This CI system is intended to generate binary installers for macOS and Windows, as well as AppImages for Linux for the set of KDE projects which support these."
Currently only a few packages (Kate, Krita, etc.) build nightly and release AppImages.
https://phabricator.kde.org/T11691
AppImageHub: https://appimage.github.io/apps/
gitlab can also build appimages. See kstars