DAOs, as any other community where humans are involved, have their own secrets. Until now only centralized solutions are being used to share sensitive information among their members such as shared online services account credentials for email, social networks, etc.
Fidelius app is named after Harry Potter's series "Fidelius charm", the spell that could be used to conceal a secret inside an individual's soul. Like in the series, Fidelius' secret keepers will be the only ones that can share the secret with new members. All the members of the DAO will be able to see who has access to each secret for transparency sake, but only those who have access (secret keepers and grantees) will be able to read them.
Organizational secrets are shared after encrypting them in the form of JSON Web Encryption (JWE). The Decentralized Identities (DID) expose methods to create and decrypt JWEs, very useful for this purpose.
Identity and public key management is handled by IDX (Ceramic Network), and the encrypted secrets are stored in IPFS.