Microsoft Teams

Microsoft Teams combines chat, meetings, file sharing and application integration, and its position comes largely from being bundled with Microsoft 365 rather than chosen on its own.

Its genuine advantage is depth of integration with Office: documents open and edit inside a channel, and identity and permissions come from the same directory that governs everything else.

Its interface is denser and its performance heavier than lighter alternatives, which is the usual complaint from teams who did not select it deliberately.