A geographic information system (GIS), also known as a geographical information system or geospatial information system, is a system for capturing, storing, analyzing and managing data and associated attributes which are spatially referenced to the Earth.

Most widely used open source applications:

• GRASS – Originally developed by the U.S. Army Corps of Engineers, open source: a complete GIS
• MapServer – Web-based mapping server, developed by the University of Minnesota.

Other open source GIS applications:

• Chameleon – Environments for building applications with MapServer.
• GeoNetwork opensource – A catalog application to manage spatially referenced resources
• GeoTools – Open source GIS toolkit written in Java, using Open Geospatial Consortium specifications.
• gvSIG – Open source GIS written in Java.
• ILWIS – ILWIS (Integrated Land and Water Information System) integrates image, vector and thematic data.
• JUMP GIS – Java Unified Mapping Platform. (See end of page for JUMP derivative projects, like Kosmo and OpenJUMP)
• MapWindow GIS – Free, open source GIS desktop application and programming component.
• OpenLayers – open source AJAX library for accessing geographic data layers of all kinds, originally developed and sponsored by MetaCarta
• PostGIS – Spatial extensions for the open source PostgreSQL database, allowing geospatial queries.
• Quantum GIS – QGIS is a user friendly Open Source GIS that runs on Linux, Unix, Mac OSX, and Windows.
• TerraView – GIS desktop that handles vector and raster data stored in a relational or geo-relational database.
• uDig