AstraChat is an enterprise chat and messaging product that provides privacy and security out of the box.
For hosting common files it's ok. Also it is on Android too do, great to transfer files between your Windows and your phone. But if you want better security you have to subscribe a monthly offer.
Mattermost - Mattermost is an open source alternative to Slack.
Dropbox - Online Sync and File Sharing
Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
Google Drive - Access and sync your files anywhere
Slack - A messaging app for teams who see through the Earth!
Mega - Secure File Storage and collaboration