Castle alternatives
TL;DR: 12 companies doing similar work to Castle in B2B, ranked by how closely they match what Castle actually does — not just by category.
How this list was built: every company here is Y Combinator-backed and shares at least one category with Castle. They are scored on how closely their own description overlaps with Castle's, and all facts shown come from the YC company records — nothing is estimated.
What are the best alternatives to Castle?
| Alternative | What it does | Batch | Team | Status |
|---|---|---|---|---|
| Fithub | — | Winter 2010 | — | Inactive |
| Insoshi | — | Winter 2008 | — | Inactive |
| Dyneti Technologies | Reduce payment fraud | Winter 2019 | 3 | Active |
| Hiro | Agents that handle security work | Summer 2023 | 2 | Active |
| Observa | Catch accidental database exposures before the bad guys | Winter 2021 | 1 | Inactive |
| PromptArmor | LLM Security and Compliance | Winter 2024 | — | Active |
| Keyri | Secure fraud prevention and authentication platform for developers | Summer 2021 | 5 | Acquired |
| AmberBox Gunshot Detection | Detect Gunshots | Inform Law Enforcement | Empower First Responders | Winter 2016 | — | Active |
| Smyte | Smyte stops bad actors on social networks and marketplaces. | Winter 2015 | 11 | Acquired |
| Stacksi | Automated Answers to Security Questionnaires | Winter 2021 | 4 | Acquired |
| CyberFend | Cyberfend delivers robust, real-time web and mobile security by… | Winter 2015 | 2 | Acquired |
| Ambient.ai | AI company transforming enterprise physical security to prevent… | Winter 2017 | 150 | Active |
Is Castle still active?
Castle is still operating, so switching is a choice rather than a forced migration. Compare on fit and price rather than urgency.
How was this list put together?
Every company here is Y Combinator-backed and shares at least one category with Castle. They are then ranked on how closely their own description overlaps with Castle's, so the closest matches come first rather than whoever happens to share a tag.