Wagn's powerful permissions system lets you set CRUD (create, read, update, and delete) permissions on any Set of cards.
These permissions are checked when a card is included. That means, for example, that if a public page includes a private card, that private card won't be shown to folks without permission. Permissions are also checked wherever cards are queried, so that search results will never turn up a card that a user doesn't not have permission to see.
Wagn also supports true file permissions, meaning that permissions are checked whenever a file is requested.