PostgreSQL describes itself as the "world's most advanced open-source database". It provides a comparatively standard and feature-rich SQL implementation based on a very stable backend server. Its open architecture makes it simiple to create and add extension modules and there is a wide range of procedural languages besides PostgreSQL's native PL/PgSQL.
PostgreSQL is an open-source project and is not backed by any one particular company, although developer funding is provided from a number of firms, including 2ndQuadrant, Enterprise DB, NTT and many more. Much code is also contributed by individuals and companies who improve PostgreSQL for their own use.
PostgreSQL was once seen the "dark horse" of the RDBMS world and although powerful was not necessarily fast nor easy to administer. The 7.x and 8.x series saw huge strides in speed and usability, and with version 8.0 introducing a native Windows port PostgreSQL became accessible to an even wider user base.
In recent years PostgreSQL has been making increasing inroads into the enterprise database market, challenging established commercial players with features such as replication, available from version 9.0 onwards, and a solid reputation for reliability. Foreign data wrappers and JSON, XML and the HSTORE key/value datatype are transforming PostgreSQL from a database into a data platform.