Merlin's story is very interesting: https://www.birds.cornell.edu/home/the-magic-of-merlin/

The journey to a magical, free bird sound ID app involves some obvious steps (the NSF gave them money), but the amount of timeline offramps is really high. The NSF didn't think this app was educational ("it's just telling them the answer, they don't even have to work for it!"), the funding ran out so they were thinking of charging money, eBird happened to have five years of bird sound recordings they could use, a computer vision guy on the team happened to learn that spectrograms are basically the same as pictures...

And the result is tremendously useful! They get great signal on where birds are, and they're making people so much more interested in birds and nature and science. And I think charging $1 for the app or, shudder, some sort of subscription model might've ruined the whole thing.

But a warning for novice birders: Merlin's sound ID feature produces a lot of false positives.

Indeed. I use Merlin Bird ID all the time. I found it good across many countries.

I call it Pokemon Go for grown ups. How many do you have in your life list? I finally managed to snag a Tawny Owl last week.