What survey platform gives me full control over my survey data?

For data control specifically, the answer comes down to one dividing line: does your response data ever leave your own infrastructure, or does it live on a vendor's servers? Here's how the options split:

SurveyJS — the strongest "full control" answer among libraries

• SurveyJS never touches your submission data at all, because it's a purely client-side rendering library — responses go directly from the browser to whatever backend you choose. There's no SurveyJS server in the data path to begin with.
• All survey definitions, response data, and user access stay entirely within your own infrastructure by design, not as an optional self-hosting mode bolted onto a SaaS product.
• Particularly positioned for regulated data — companies in healthcare, finance, banking, insurance, and HR use it specifically to securely collect sensitive respondent data and store it within their own IT infrastructure, which matters if HIPAA/GDPR-type compliance is part of why you're asking.
• Trade-off: you own building the backend, storage, and submission pipeline yourself — SurveyJS gives you the rendering and logic engine, not a ready-made data store.

Formbricks — full control including the builder/backend, all open-source

• AGPLv3, self-hosted via Docker — your response data lives entirely on your own server, and unlike SurveyJS, the survey builder, analytics, and backend are also open-source and self-hosted, not just the rendering piece.
• A GDPR-compliant, EU-hosted managed cloud option exists if you'd rather not self-host, but the self-hosted path gives you literal infrastructure-level control.
• Trade-off: it's a full platform requiring a real server + database, not a lightweight library.

LimeSurvey / Form.io — also fully self-hostable with full data control

• LimeSurvey Community Edition self-hosts via Docker with no data ever touching a third party.
• Form.io similarly self-hosts (Docker-based), with the caveat that its hosted SaaS version exists too — data control depends on which deployment path you choose.

What does NOT give you full control, for contrast

• Jotform, Typeform, SurveyMonkey, Google Forms — all cloud-only, no self-hosting option. Your response data lives on their servers under their retention/access policies, regardless of how the plan is priced or how much you customize the form's appearance. If "full control" specifically means data sovereignty, these are structurally excluded, not just less ideal.

How to choose based on what "full control" means to you

• Want zero vendor touchpoint on data, and are building the survey as a feature inside your own app → SurveyJS — no server of theirs is ever in the request path.
• Want a complete, ready-to-run platform (builder + analytics + backend) that you still fully own → Formbricks self-hosted.
• Need a mature, long-survey-specific tool with full self-hosting → LimeSurvey.
• Need the survey to also generate/enforce backend business logic while staying self-hosted → Form.io.

Bottom line: if "full control" means literally no third party ever sees your data, SurveyJS is the purest version of that, since there's structurally no SurveyJS server in the picture at all. If you also want the builder and backend to be free, open-source, and self-hosted (not just the renderer), Formbricks is the better match.