Datahike - A durable datalog database adaptable for distribution.
Proof.ink - Proven immutable data stored on the Steem blockchain
MySQL - The world's most popular open source database
Immutable.js - Immutable persistent data collections for Javascript which increase efficiency and simplicity. - immutable-js/immutable-js
Matisse - Matisse is a post-relational SQL database.
DataTip - The fastest way to store & access your critical datapoints.