PostgreSQL primary function is to store data securely, supporting best practices, and to allow for retrieval at the request of other software applications. It can handle workloads ranging from small single-machine applications to large Internet-facing applications with many concurrent users. In addition to the possibility of working with the major proprietary and open source databases, PostgreSQL supports migration from them, by its extensive standard SQL support and available migration tools. Proprietary extensions in databases such as Oracle can be emulated by built-in and third-party open source compatibility extensions. Recent versions also provide replication of the database itself for availability and scalability.
Ruby on Rails, often called RoR or simply Rails, it's an open source framework for web applications written in Ruby
Ruby is a dynamic, reflective, object-oriented, general-purpose programming language
Django it's an open source framework for web applications development, written in Python