I thought it's like a Shazam for bird sings. Record a bird, send it and get the answer what it is.
It runs live on your phone so you don't have to send anything and pops up bird identification as it hears the songs. Merlin can also do photo ID and ID by asking 5 simple questions which are matched with GPS and eBird results.
The companion app, eBird, is the comprehensive bird tracking app from Cornell, the leaders in orinthology.