Well offline. Not really. Unless you would prefer jailbreak.
You have 3 options:
- Distribute via AppStore (free, but everybody can download)
- Distribute via AppStore B2B (volume pricing, not available for all countries)
- Via Enterprise Setup
- Adhoc
ad. 1 & 4
Im sure you you thought of these options.
ad. 2
Distribute via AppStore, https://developer.apple.com/programs/volume/b2b/
Custom apps are distributed privately to authorized Volume Purchase Program for Business members that you identify in iTunes Connect. Customers sign in and purchase their apps on the Volume Purchase Program store.
Im not sure about option 2, but it might be that Apple will still be reviewing the app. If you choose Enterprise dist. Apple will not review your app. and you need to setup your own infrastructure.
ad. 3
/* this is on a per company basis, you can't setup your
own enterprise account and start distribution
to *different* companies. */
I have implemented this for a customer. They have a enterprise subscription. Then they invited me as a team member. I can sign the IPA file with the correct certs.
We choose (< 30 devices)to install via a webpage. Its has a install link. There a 2 files you need. A PLIST and the Binary (IPA). The PLISt files contains the URL to the IPA file. Once i place a update, they need to manual install this on each device.
If you like you can also just type the plist link directly in safari, or make "app bookmark".
You can push the app to all devices (Mobile Device Management (MDM)), but (as far as i know) you need a more advanced setup. I never looked into this.
Since iOS 6 the files needs to be server from a HTTPS connection! I have setup a self sign certificate (since the server is running on a LAN), and we then installed the HTTPS certs on each device. You could bypass the certs issue by putting the files on something like dropbox (or by official certs)