Keybase

About

Keybase is secure messaging and file-sharing for work or personal use. It uses public key cryptography to keep your messages private, and the website says even Keybase can't read your chats. Keybase also works for families, roommates, clubs, and groups of friends. You can create teams with anyone and connect to public identities from communities on Twitter, Reddit, and elsewhere.

Groups can store and share photos, videos, and documents with end-to-end encryption. For especially sensitive conversations, you can set a timer on messages to send exploding messages.