Slack

Slack is a messaging platform for organisations, organised around channels. A channel is a named conversation that can be public, private, or shared with an external organisation, and membership is a deliberate act rather than an accident of a contact list. The structure is what distinguishes it from a group chat. Threads keep a reply attached to its parent, so a channel is not consumed by a side conversation. Search covers message history and files, and a shared channel lets two organisations work in the same space without exchanging accounts. The platform's second half is the app directory and workflow builder. Incoming webhooks, slash commands, and bots let an external system post into a channel or accept a command from one, which is how alerts and approvals end up where a team already is. The cost is per-seat pricing and the fact that an organisation's conversation history lives in a vendor account.