Grist [1] is an "augmented" but still "classic" relational DB builder. It is (kind of) open-source, backed by SQLite, and you can self-host it. I like it because it is user-friendly while also being highly programmable (Python formulas, widget grid) and "data-friendly" (nice filters, Merge imports...)
Tana [2] is a less classic kind of DB. The main view is an "advanced" outliner (like Roam). But every line of text could also act as an "universal Form" and a "node" in a semantic graph DB. Wherever and whenever you type, you can turn your unstructured, freeform blocks of text into "as you go" structured data. This works well for Evergreen-Notes [3], Tasks, Contacts...
A bonus : for any kind of references (and not just citations), Zotero is very flexible. As local/opensource personal DBs go, it is a solid bookmark manager and pdfs-annotations store.
[1] https://www.getgrist.com/ [2] https://tana.inc/ [3] https://maggieappleton.com/evergreens