The Pick OS and its many derivatives had a non-relational database based on hashing at the core of the OS. Very popular a few decades ago but mostly dead now.

The Pick OS and its many derivatives had a non-relational database based on hashing at the core of the OS. Very popular a few decades ago but mostly dead now. I do miss embedded SQL. The mismatch between database types and application language types caused by separating the two leads to lots of boilerplate and subtle bugs and logical inconsistencies.