Firstly, thanks for the software - I downloaded it on impulse, but it's now running pretty much all the time on my macbook - I find it very easy to create a soundmix which makes for a much more pleasant working environment, so I've commented & rated it accordingly on the appstore.
But...... nice as it is, I think it's an app which is on the verge of greatness, just not quite there yet.
I realize other people may use the app for different purposes (soothing kids etc.), but I do think you could get an awful lot of people using it just like me, to make a handful of sound mixes for ambient background sound while they're working, reading, whatever. Instead of thinking of individual sounds, you need to think in terms of different soundscapes (and whether you have enough sounds for variety in each one - Beach, Forest, Indoors etc.) Here's what I think:
1. You need more sounds! ( One Amazon rain forest? I want three. Likewise, Thunderstorms, Cars passing, Birdsong, Clock ticking and so on. Water dripping - great, but it's too fast. Light rain - good, but lose the irritating birds. I want quiet conversation & the clattering of coffee cups in a pavement cafe. I just want more!). Even considering different tastes, I don't think you need hundreds more - maybe 50 would be plenty.
2. Could you approach sound engineers to submit samples? (then you won't have to worry about copyright). Try the BBC in the UK (80 years of public service broadcasting and a huge sound library). There must be sound engineers who have kids to soothe who would appreciate a free copy of the app, and mention on a credits page? (and, by the way, if you do get more sounds, you'll need a way to group them)
3. The playlist is good but there's a gap between sounds - I want a way to fade them seamlessly into each other. And I want to loop the playlist.
4. I want to name my soundmixes (or tag them), so I can tell which is which.
5. Why don't you include a link in the app to a questionnaire, to find out how people are actually using it? Offer a small prize, and you might get a lot of useful feedback
That's probably enough for now. I'll shut up (I don't usually comment on software, but you've got me interested)