I wrote a simple dynamodb style database with a python dictionary and a Google pygtrie ("trie" data structure)

It's still a toy but I kept adding features.

I then kept working on it and added distribution with consistent hashing, rudimentary SQL joins, Cypher graph database queries and document storage. You can even query documents with SQL.

I didn't get around to changing the graph storage to be multimodal.

It takes very little code to write something with lots of features.

https://GitHub.com/samsquire/hash-db

There's an AVL tree that farleyknight wrote and a btree that I wrote that need to be integrated into it.