Relational Database
Microsoft SQL Server - a relational database management system developed by Microsoft.
MySQL - an open-source relational database management system (RDBMS). Released under GPL license.
PostgreSQL - free and open-source relational database management system (RDBMS) emphasizing extensibility and SQL compliance. Released under PostgreSQL license, a liberal Open Source license, similar to the BSD or MIT licenses.
Non-relational Database
MongoDB - a cross-platform document-oriented database program. Classified as a NoSQL database program, MongoDB uses JSON-like documents with schema.
Mongoose.js - elegant mongodb object modeling for node.jsRedis - Redis stands for Remote Dictionary Server, and is an in-memory data structure project implementing a distributed, in-memory key–value database with optional durability. Released under BSD license.