This is “Cuckoo Clock”.
When this app running, Cuckoo sing every hour and every 30minutes.
When you want hear Cuckoo Singing, press the switch button inside of bottom.Cuckoo Singing about 30 Hour. If you don’t need Cuckoo, please switch off again.

You can change Alarm mode and Custom. And can buy add-on for additional sounds, background images also remove Ad.