Best Slack Alternative 2026: Mattermost vs Microsoft Teams vs Discord for Work Teams

The best Slack alternative depends on what you're replacing and why. Microsoft Teams (included in Microsoft 365) wins on total value if your organization is already in the Microsoft ecosystem — it's effectively free and covers video calls, file storage, and collaboration. Mattermost wins for self-hosted, privacy-focused, and security-conscious organizations (government, healthcare, finance) who want to own their data and run air-gapped deployments. Discord wins for developer communities, gaming teams, and async-first organizations that value community features and free voice channels. Slack remains the default for product and tech companies that haven't yet felt the pricing pressure.