Slack

Slack is the default team messaging tool for most overseas companies, organizing conversation into channels by project, team or topic rather than into individual threads.

Its real strength is integration: build alerts, deploy notifications, support tickets and monitoring can all post into the channel where the relevant people already are, which is why it often becomes an operational hub rather than just a chat app.

The free tier limits message history, which is the practical reason most teams eventually pay — searchable history is where much of the accumulated value sits.