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
There are 2 ways of doing this.
Enable if you used the UI to configure HACS
Add a checkmark to the left of AppDaemon apps in the UI configuration for HACS.
For more about configuring HACS with the UI have a look here
Enable if you used YAML to configure HACS
If you used YAML to configure HACS, add this under your HACS configuration to enable AppDaemon apps:
hacs:...appdaemon: true
After adding that you need to restart Home Assistant.
For more about configuring HACS with YAML have a look here
AppDaemon apps download location
Any AppDaemon app downloaded with HACS is stored in appdaemon/apps/ in your Home Assistant configuration directory.