It depends on your definition of "free". Some well known open-source approaches are:

Mattermost: An open-source, self-hosted communication platform that offers features such as file sharing, live chat, video calls, and screen sharing.

Jitsi Meet: A free, open-source video conferencing platform offering features like screen sharing, audio and video calls, and file sharing.

It's not free, but typical for a corporate environment are the communication tools from Microsoft O365 and Google Workspaces.
spam fails_task lang_mismatch pii not_appropriate hate_speech sexual_content quality toxicity humor helpfulness creativity violence