This sounds a lot like Athens Research[1] vs Roam Research[2]. Jeff Tang wanted to get a job at Roam so he built a toy open source version for themselves, and then continued and it's now a YC company [3]

[1]: https://www.athensresearch.org/

[2]: https://roamresearch.com/

[3]: https://www.ycombinator.com/companies/athens-research