Even if you manage to get a working app without using Apple's development kit, you can't sideload on iPhones or iPads. Well, you can if you jailbreak/root, but that's a different can of worms.
If it's a Mac app, archive your app bundle in Xcode and select distribute, then "Copy App" and just send the app bundle.
If it's for iOS, watchOS, etc. you can send over the entire Xcode project and have them build it to their device on their own, though they will need to regularly re-sign it
If it's for iOS, watchOS, etc. you can send over the entire Xcode project and have them build it to their device on their own, though they will need to regularly re-sign it