Called Keybase Teams, the fully encrypted platform supports groups as large as 500 people, with free access to a team's message history.
Keybase is a new and free security app for mobile phones and computers. For the geeks among us: it's open source and powered by public-key cryptography. Keybase is for anyone. Imagine a Slack for the whole world, except end-to-end encrypted across all your devices. Or a Team Dropbox where the server can't leak your files or be hacked.Like Slack, once users have created a team in Keybase they can begin generating chats and channels. It's also possible to share encrypted files with team members.
Unlike Slack accounts however, users don't have to switch at the top level of the app. Teams can be casual and small, allowing them to blend into the user's inbox, while teams with multiple chat channels are grouped under "Big teams".
Keybase Teams is a free download for Mac from the Keybase website, while the Keybase chat app is available for iPhone and iPad on the App Store. [Direct Link]