People already know that reliable databases such as MySQL, PostgreSQL, MSSQL, SQLite, and MS Access. But there are many databases that can be used, even free and open source

1. MariaDB

MariaDB

MariaDB is a backward compatible, drop-in replacement branch of the MySQL® Database Server.
It includes all major open source storage engines + the Maria storage engine.

2. MonetDB

MonetDB

MonetDB is a database system for high-performance applications in data mining, OLAP, GIS, XML Query, text & multimedia retrieval.

3. MongoDB

It is an open source, high-performance, scalable, schema-free & document-oriented (JSON-like data schemas) database.
There are ready to use drivers for most popular programming languages like PHP,Python, Perl, Ruby, JavaScript, C++ + more.

4. Apache CouchDB

Apache CouchDB

A document-oriented database that can be queried and indexed in a MapReduce fashion using JavaScript.
CouchDB offers a RESTful JSON API which can be accessed from any environment allowing HTTP requests

5. Oracle Berkeley DB

Oracle Berkeley DB

It is an embeddable database engine that provides developers with fast, reliable, local persistence with zero administration.
Oracle Berkeley DB is a library that links directly into your application & enables you to make simple function calls rather than sending messages to a remote server for a better performance.