Ask HN: Are there any open source A/B testing tools?

Not open-source (as you have to initially pay for a license), but it is self-hosted: you can try out my analytics platform[0] as it has an A/B testing feature and you can always implement your own A/B versions and just track stats for each of them.

Let me know if you have any questions or concerns about userTrack!

[0]: https://www.usertrack.net

A fair number of Web frameworks have OSS A/B or multivariate testing tools: https://github.com/topics/ab-testing. In the Ruby world, splitrb (https://github.com/splitrb) and vanity (https://github.com/assaf/vanity) are popular.

Google Optimize is the only 0 cost and hosted tool that I've seen. Unfortunately, you're giving more data to Google. Most a/b tools quickly evolve into paid due to the nature of their complexity and users.

VWO is probably your best bet for low cost and not Google.

Matomo is open source but the A/B testing plugin costs 200 euros a year after a 30 day trial period.

I would most likely just cobble together something with nginx and serve two separate versions of the content and measure the metrics you desire separately.