If you're interested in the idea of databases built from scratch since the time this post was written in 2017 (based on GitHub contributions info), here are a few:
- Materialize: 2017
- DuckDB: 2018
- RedPanda: 2019
- TigerBeetle: 2020
KùzuDB[1] is an in-process graph database built from scratch and came out of academia too. We are from Data Systems Group at University of Waterloo, started since Sep 2020, and have a small team actively work on it now.
These two posts[2,3] explain where we are from and where we're going, if anyone is interested.
[1]: https://github.com/kuzudb/kuzu
[2]: https://kuzudb.com/blog/meet-kuzu.html
[3]: https://kuzudb.com/blog/what-every-gdbms-should-do-and-visio...