Best / A/B testing
Best open-source A/B testing
The best self-hosted A/B-testing split in the c17.io catalog is GrowthBook for MIT-core flags and experiments (the published Optimizely stack — skip enterprise/; GitHub license field is Other), Unleash when the job is AGPL-3.0 feature flags rather than an experiment UI — /compare/growthbook-vs-unleash, Flagsmith when you want that BSD-3-Clause flag API — /compare/unleash-vs-flagsmith, and PostHog when experiments sit next to funnels. This is not Optimizely's every personalization SKU. Heatmaps stay on /best/heatmaps.
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Ranked picks
1
GrowthBookMIT core experiments (skip enterprise/) — the c17 Optimizely path. /compare/growthbook-vs-unleash.
When to pick it: A flag and a controlled test you host.
8,521 stars in the catalog
2
UnleashAGPL-3.0 feature flags already on /best/feature-flags. Not an Optimizely desk.
When to pick it: Toggles, not a multivariate page test.
13,891 stars in the catalog
3
FlagsmithBSD-3-Clause flags already on /compare/unleash-vs-flagsmith.
When to pick it: The BSD sibling if Unleash is not the API.
6,610 stars in the catalog
4
PosthogProduct analytics with experiments already on /best/product-analytics.
When to pick it: A test next to a funnel, not a standalone experiment OS.
How they compare
| Tool | License | Self-host | Best for |
|---|---|---|---|
| GrowthBook | Other | Medium | A flag and a controlled test you host. |
| Unleash | GNU Affero General Public License v3.0 | Medium | Toggles, not a multivariate page test. |
| Flagsmith | BSD 3-Clause "New" or "Revised" License | Medium | The BSD sibling if Unleash is not the API. |
| Posthog | Not listed | Medium | A test next to a funnel, not a standalone experiment OS. |
Related pages
- GrowthBook stack
- Unleash / Flagsmith stack
- PostHog stack
- Replace Optimizely
- Replace VWO
- Replace LaunchDarkly
- Replace Split.io
- Replace ConfigCat
- Replace Statsig
- Replace Hotjar
- Replace Amplitude
- Replace Heap
- Replace FullStory
- Replace LogRocket
- Replace PostHog Cloud
- Replace Pendo
- Replace Smartlook
- Replace Mouseflow
- Replace Crazy Egg
- Replace Lucky Orange
- Replace Microsoft Clarity
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FAQ
- GrowthBook or Unleash?
- GrowthBook if you want the published Optimizely experiment path. Unleash if the job is a flag — /compare/growthbook-vs-unleash.
- Optimizely, VWO, or AB Tasty?
- This page publishes Optimizely — /replace/optimizely. VWO is the same published experiment — /replace/vwo. AB Tasty was skipped so the lander stays one path.
- Is this a heatmap?
- Heatmaps stay on /best/heatmaps. This page is an experiment.
- Are these free?
- GrowthBook core is MIT if you skip enterprise/. Unleash is AGPL-3.0. Flagsmith is BSD-3-Clause. You pay hosting. Template users never pay c17.
- How do I deploy it?
- Open /stacks/growthbook-experiments. Persist the database. Create one experiment.
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