AppDaemon apps are apps for AppDaemon.
Since not all users are running AppDaemon, AppDaemon is not enabled by default in HACS.
Enable AppDaemon apps in HACS
Add a checkmark to the left of "Enable AppDaemon apps discovery & tracking" in the UI configuration for HACS, then click Submit.
See the documentation for more information about configuring HACS.
AppDaemon apps download location
Any AppDaemon app downloaded with HACS is stored in
appdaemon/apps/ in your Home Assistant configuration directory.