No need to introduce it. The reference for your internal communications.
The ultimate gamer chat, which can also be used by work teams.
Formerly appear.in, this is another alternative for making video calls,
Learn a language, with someone from another country. Really great.
The reference for video calls. Special mention to the recording of separate tracks, useful for podcasting in particular.
The best alternative to Slack, with the advantage of being less "present".
Google's video conferencing tool. All good.
The alternative to Slack, by Microsoft.
Create or integrate a chat on your site or app without coding. The must is the use of credits to be able to chat, ideal for online training platforms.
Another very good open source alternative to Slack. Less integrations but some are welcome like the one with Trello or GitLab.
The open source alternative to Slack. Less features, but on your servers.