Proton and Apple are mature, audited, and battle-tested — if you want proven-today encryption, they’re excellent, and we say so below by name. Cornerstone is new, and its bet is different: one private place for a family’s whole digital life — a family AI you can actually ask, an encrypted vault for photos and documents, kid access with parent oversight, a device mesh and backup — under one rule, honest custody: the server holds only ciphertext and refuses to receive your key. Where the mature players are ahead, the table says so plainly.
| Feature | Cornerstone us | Proton | Apple iCloud+ | Google One | Synology (home NAS) |
|---|---|---|---|---|---|
| End-to-end / zero-knowledge encryption | ✓ | ✓ | •ADP opt-in | ✗ | •self-configured |
| Independently audited / proven today | •no (new) | ✓ | ✓ | ✓ | ✓ |
| Encrypted vault for photos + documents | ✓ | ✓ | •ADP | ✗ | •self-configured |
| "What the server sees" proof panel | ★only here | ✗ | ✗ | ✗ | — |
| Private family AI you can ask | ★only here | ✗ | ✗ | •cloud AI | ✗ |
| Age-graded kid access + parent oversight | ★only here | ✗ | •Screen Time | •Family Link | ✗ |
| Cross-platform (not locked to one vendor) | ✓ | ✓ | •Apple-first | ✓ | ✓ |
| Device mesh across the home | •building | ✗ | ✓ | ✓ | ✓ |
| Encrypted cold / off-site backup | •building | ✗ | ✓ | ✓ | •self-configured |
| Self-host / run it on your own box | •roadmap | ✗ | ✗ | ✗ | ✓ |
| No subscription required | ✓ | ✗ | ✗ | ✗ | ✓ |
| Your data is not the business model | ✓ | ✓ | ✓ | ✗ | ✓ |
Prices verified August 2026. ✓ yes · ✗ no · ★ only here · notes are literal.