ActiveOrient @ GitHub
OrientDB is a Multi-ModelDatabase. Its community Release is OpenSource, the Company has just been bought by SAP. Version 3 is released in autumn 2018. The unique feature: SQL is used to query a NOSQL-DB
ActiveOrient aimed to be the ActiveRecord equivalent to the NOSQL-World – but it has gone its own way.
Still – Database tables are manged like AO-Models and integration to ruby projects is similar.
There is a wiki: https://github.com/topofocus/active-orient/wiki