TL;DR
Best open source A/B testing tools: GrowthBook (best pure A/B testing), PostHog (best all-in-one with analytics), Unleash (best feature flags). Open source = full data control but requires DevOps. For most teams, a SaaS tool like ExperimentHQ is simpler and more cost-effective.
Tool Comparison
| Tool | License | Visual Editor | Statistics | Verdict |
|---|---|---|---|---|
| GrowthBook | MIT | — | Bayesian | Best Overall |
| PostHog | MIT | — | Frequentist | Best All-in-One |
| Unleash | Apache 2.0 | — | Basic | Best Feature Flags |
| Flagsmith | BSD 3-Clause | — | Basic | Good Alternative |
Pros
- • Full data control—your servers, your data
- • No vendor lock-in
- • Customizable to your needs
- • Free (hosting costs only)
Cons
- • Requires DevOps to set up and maintain
- • No visual editor (usually)
- • You're responsible for uptime
- • May lack advanced features
Open Source vs SaaS: True Cost
Open source isn't always cheaper:
- • Hosting: $50-500/month for servers
- • DevOps time: Setup, maintenance, upgrades
- • Opportunity cost: Time spent on infra vs testing
- • SaaS alternative: ExperimentHQ at $29/month with zero maintenance
Our Recommendation
If you need open source: GrowthBook for A/B testing, PostHog for analytics + testing.
For most teams: ExperimentHQ is simpler at $29/month with visual editor and zero maintenance.