PiSi is a modern package manager for UNIX systems. It has been designed to meet the requirements of the Pardus Linux distribution, and it is not derived from any other package manager. It is efficient and small. Package sources are written in XML and Python. Fast database access is implemented with Berkeley DB. It integrates both low-level and high-level package operations. Sources can be maintained easily through a version control system as original sources do not have to be copied. It uses a framework approach to build applications and tools upon. It has both a comprehensive CLI and a user-friendly Qt-based GUI.