Encryption is not the difference
Vaultaire and Vaultine both encrypt with AES-256-GCM, unlock with a 5x5 pattern and need no account. Encryption is not what separates them. Two things do.
Every pattern opens a vault
This is the interesting one, and it is Vaultaire's own description of its design rather than our characterisation of it. Its homepage states that every pattern opens a different vault and that there is no master list, no vault count, and no proof other vaults exist. Its manifesto adds that entering the wrong pattern produces no error — just an empty vault — because there is no observable difference between "wrong" and "empty".
It also has a consequence worth understanding before you choose it. If anyone picks up your phone and draws a pattern, they get a working vault and can put things in it — and you have no way to find out, because the app keeps no list of vaults to show you. That is not a bug; it follows directly from the feature.
Vaultine works the other way round. An unrecognised pattern or PIN is rejected and nothing opens. The vaults on your device are exactly the ones you created, and your Decoy Vault contains exactly what you put in it. You always know what is on your own phone.
Deliberate versus emergent deniability
Both apps answer the same question — what happens when someone makes you unlock — with different mechanisms.
Vaultaire's answer is emergent. Show any pattern, get any vault, and there is nothing to contradict you.
Vaultine's is prepared. The Decoy Vault opens on a second code and shows a vault you stocked in advance, so you know precisely what is revealed. The Duress Vault opens on a third code, shows an empty vault, and wipes your real vaults as it does. Once it has, that vault becomes your main vault, so there is no empty shell left sitting there to explain. You configured both, so neither can surprise you.
With Vaultine you decide in advance what a search will turn up. With Vaultaire, nobody can tell what is on the phone, not even you.
One vault, four platforms
Vaultaire is an iPhone app. Vaultine runs on Windows, macOS, iOS and Android today, so the documents on a laptop get the same vault as the photos on a phone. In a category that is almost entirely mobile-only, this is the difference that tends to decide it.
