This category covers chat and team communication: messengers, team chat platforms, social network clients and IRC. Many desktop apps are wrappers around web services, so check whether an app is a native client or an Electron wrapper, which affects memory use and how notifications behave.
Signal Desktop and Telegram are official desktop clients for their messengers, while Mattermost is an open source, self-hostable alternative to Slack. Rambox and Ferdium combine many web messaging services in one window. For IRC, Textual and LimeChat are native Mac clients. If privacy matters, prefer open source clients and services with end-to-end encryption.