alt Hacker NewsMatrix is good as a LiveKit client who support active call, like a phone call, and good enough for passively share screen (no remote input supported for now). Not good for chat.
A good FLOSS internal chat is Zulip, a passable one is Mattermost (who is better for many things, but being "Open Source Enterprise" is largely a no-go IMO.
Zulip+DocMost are Slack+Confluence. Zulip support calls as well, but via Jisti and they aren't much nice IMO.
I know that Mattermost came with Gitlab, but didn't like it at the time (but that was like 6-7 years ago, so it might have been better). We were somewhat spoiled with how good Telegram desktop application was/is, so at the time didn't want to move. However, as the company grows and its processes become more complex, a simple chat application is no longer sufficient. We need a more integrated collaboration platform that connects seamlessly with Jira and other company systems, supporting our organizational structure, workflows, and policies.
Will look into Zulip, thx.