Slack

Slack is a messaging platform for work. Teams communicate in channels organised by project, topic or team, alongside direct messages, threads, audio and video huddles, and integrations that bring notifications and actions from other tools into the conversation. Slack is owned by Salesforce. It changed how many companies communicate internally. Before Slack, most workplace communication happened in email, which is slow, siloed in individual inboxes and poor for group discussion. Channels made conversations searchable, transparent and open to anyone who needed context, and Slack's friendly design and integrations made it the default communication hub for technology companies and, increasingly, organisations of every kind. Integrations are a core strength. Thousands of apps connect to Slack, so engineers see deploy notifications and incident alerts, support teams get escalations, sales teams see deal updates, and bots answer questions. Workflow Builder automates routine processes such as approvals and onboarding without code. Slack Connect extends channels to external organisations, letting companies work with clients, agencies and vendors in shared channels instead of long email threads, which has become a common way for B2B companies to support major customers. Slack AI summarises channels and threads, answers questions from workspace history and powers AI agents that can take actions. The free plan limits message history visibility to a recent window and restricts integrations, pushing growing teams to paid per-user plans. Common criticisms concern notification overload and the always-on culture that real-time messaging can create, along with costs for large organisations. Alternatives include Microsoft Teams, bundled with Microsoft 365 and dominant in large enterprises; Google Chat for Google Workspace organisations; Discord for communities and some startups; Mattermost and Rocket.Chat for self-hosted, security-focused deployments; Zulip for topic-threaded conversations; and Twist for calmer, asynchronous communication. Choose Slack when you want the most widely adopted, integration-rich messaging hub for your team. Choose Teams if your organisation already runs on Microsoft 365.