MySQL is a free DBMS for relational database systems. MySQL was originally developed to improve performance handling of large databases. This database management system with open source was created as an alternative to commercial systems. MySQL was originally very similar to mSQL, but over time it has been expanding and now MySQL is one of the most popular database management systems. Primarily it is used to create dynamic Web pages because it has excellent support from various programming languages.
PostgreSQL is an object-relational database management system (DBMS). It is an alternative as for commercial DBMS (Oracle Database, Microsoft SQL Server, IBM DB2 and others) as for the open source DBMS (MySQL, Firebird, SQLite). Compared with other open source projects such as Apache, FreeBSD or MySQL, PostgreSQL is not controlled by any company, its development is possible through the cooperation of many people and companies that want to use the database and introduce her latest achievement.
MariaDB – is a MySQL DBMS fork, developed by the community. It was created resolving the need to provide the free status of DBMS (licensed under GPL), as opposed to an uncertain Licensing Policy MySQL by Oracle. MariaDB refused from InnoDB storage engine and replaced it with XtraDB. It also included Aria, PBXT and FederateX storage engines.
MongoDb is a document-oriented database. It means, that each record is a document without rigidly specified circuit that can contain nested documents. MongoDb has high speed of reading, writing, zooming. For example, MongoDb has excellent implementation of replication, which is quite easy to install and highly configurable or shardinh (the ability to spread data across multiple servers), which is also very easy to install. In complex, you can get a system of distributed computing with high failure resistance.
Redis (REmote DIctionary Server) – an open source network data warehouse which store data as “key – value”. It is high-performance, non-relational database engine (DBMS). It performs point-in-time snapshots of the dataset at specified intervals. Using Redis, the application can create channels, subscribe to them and put into the channels of communication, which will be received by all subscribers. Redis supports data replication. Redis also supports transactions and batch processing commands. Redis is written in ANSI C and works in most POSIX systems like Linux, *BSD, OS X without external dependencies.
SQLite – a lightweight relational database management system which is contained as a library, where list of SQL-92 standard statements are implemented. Source of SQLite is distributed as public domain and it can be used without restrictions for any purpose. The financial support of SQLite Developers Community provides consortium, which is specially created, and it includes such companies as Adobe, Oracle, Mozilla, Nokia, Bentley and Bloomberg.