Audulus 3 – Almost certainly one of the most complete, and also complex modular synths for iOS
This is a big app and a massively capable app too. Users have made some truly amazing patches for Audulus. If you check the forum there’s well over 600 there which you can download. There’s also lots of tutorial videos and even live streams too. But this is a complex app and you will need to take time to learn how it works to get the best value for your $19.99 on the app store.