Your games.
Your phone.
Three emulators for iPhone and iPad, and iGBA on Android too. No games are included: you import the files you already own, and everything runs on the device.
How these apps work
Nothing is bundled. The apps ship without game files and never link to any. You import files you already own from the Files app, iCloud Drive or a folder on your device.
eNDS is open source. Its code is published at github.com/mattiaa95/eNDS.
On the device. Saves, save states and cheats stay on your phone. There are no accounts and no servers. Privacy policy.
Questions. 30 of the questions people actually ask, answered on the support page.