Mattermost!

REQUIRES MATTERMOST SERVER v4.0+Older servers will not be able to connect. Mattermost is secure workplace messaging from behind your firewall.- Discuss topics in private groups, one-to-one or team-wide- Easily share and view image files - Connect in-house systems with webhooks and Slack-compatible integrationsTo use this app, you need a URL for a Mattermost server. Host your own server: https://about.mattermost.com/download Terms of Service: http://about.mattermost.com/terms/ Contribute to the project: https://github.com/mattermost/mattermost-mobile