I would also like the source code for the iOS app:
NTAG I2C Demoboard on the App Store
Especially because the app includes password protection, which I'm curious about how this was implemented. NTAG I2C does not support ISO7816 or ISO15693 (for sending commands via Apple's Core NFC framework), so was NDEF used?
I was able to find a fairly recent document on the Android app from May, 2020:
https://www.nxp.com/docs/en/user-guide/UM10966.pdf
And source code (however from 2016):
NTAG I²C Demo Android App Source code
I would really appreciate an update regarding iOS since Core NFC (starting with iOS 13) now supports read/write and tag specific APIs!