Unleash is open source (Apache 2.0 License). Repo: https://github.com/Unleash/unleash .

Growthbook (as mentioned in a sibling comment) is also open source (MIT License). Repo: https://github.com/growthbook/growthbook

Would be interested in knowing the feature differences between the three as they are all Node / Typescript projects

Great points! I think the main differentiation for us is the connection to pricing and billing. Let’s say you have a feature like “how many seats (users) this customer has” it’s not enough to just be able to define it and fetch it where’ve you need it - which is basically what the tools you mentioned will give you. It depends on which pricing tier the customer’s in. Maybe they bought 5 seats but then 2 more as an add on on top of it. Maybe you want to allow them to use more seats, but just bill them accordingly.

Does it make sense?

Or another yc company Growthbook