OpenProject vs Slack: Complete Comparison (2026)

Why choose OpenProject

• Higher Cost score (8/10 vs 5/10)
• Higher Analytics score (6/10 vs 3/10)
• Better fit for government (8/10 vs 6/10)
• Includes Gantt charts, which Slack lacks
• Includes Time tracking, which Slack lacks

Why choose Slack

• Higher Integration score (10/10 vs 5/10)
• Higher Ease of Use score (7/10 vs 5/10)
• Better fit for startups (8/10 vs 4/10)
• Better fit for small business (8/10 vs 5/10)

OpenProject

Pros

• The free self-hosted Community edition is GPLv3 open source and shares one codebase with the paid editions.
• It hosts cloud data in the EU, encrypts it with AES-256 at rest, and offers a signable GDPR data processing agreement.
• It supports classic Gantt planning and agile boards and backlogs in the same tool.
• Time and cost tracking with budget reports is built in.
• Long contract terms carry large discounts, for example fifteen months free on a five-year term.

Cons

• Paid plans require at least 25 users, and Premium requires 100.
• Several Reddit users report that self-hosted installation is hard, and some find the tool too elaborate for simple needs.
• Slack, Toggl and Mattermost connections are unsupported community plugins.
• Reviewers say the interface is less polished than tools like Asana, and that resource and workload management is weak.
• Many features, including SSO and portfolio management, require paid Enterprise tiers.

Slack

Pros

• The app ecosystem is very large, and tools such as ClickUp, Notion, HubSpot and Clockify can post updates into channels.
• Slack Connect lets teams work in shared channels with up to 250 outside organizations on paid plans.
• Compliance coverage is broad, including ISO 27001, SOC 2 Type II, FedRAMP Moderate and HIPAA configurability.
• Lists add table and board layouts with assignees, due dates and subtasks, without leaving chat.
• Workflow Builder automates routine requests and approvals without code.

Cons

• There are no native Gantt charts, dependencies, time tracking or portfolio reporting, so Slack doesn't replace a dedicated PM tool.
• Frequent notifications and busy channels can interrupt focus, a common complaint in reviews.
• The free plan keeps only 90 days of message history and allows 10 apps.
• Advanced AI features require Business+ or above, and per-user costs add up as teams grow.
• Reviewers report that finding older messages through search can be difficult.