GRASS GIS!

QGIS, formerly Quantum GIS, is a user friendly open source Geographic Information System (GIS) licensed under the GNU General Public License that runs on Linux, Unix, Mac OSX, and Windows and supports numerous vector, raster, and database formats and functionalities.

PostGIS adds support for geographic objects to the PostgreSQL object-relational database. In effect, PostGIS "spatially enables" the PostgreSQL server, allowing it to be used as a backend spatial database for geographic information systems (GIS), much like ESRIs SDE or Oracles Spatial extension. PostGIS follows the OpenGIS "Simple Features Specification for SQL" and has been certified as compliant with the "Types and Functions" profile.

ArcGIS is geographic information system (GIS) software for visualizing, managing, creating, and analyzing geographic data. Using ArcGIS, you can understand the geographic context of your data, allowing you to see relationships and identify patterns in new ways.

Mapnik is a Free Toolkit for developing mapping applications. Above all Mapnik is about making beautiful maps. It is easily extensible and suitable for both desktop and web development. - C++/Python GIS toolkit

The reference implementation of the Open Geospatial Consortiums WFS and WMS services, GeoServer is a full featured open source software server written in Java that allows users to query, visualize, combine, edit and publish spatial data over the web.

OpenLayers is a high-performance, feature-packed library for all your mapping needs.

gvSIG is a Geographic Information System (GIS), that is, a desktop application designed for capturing, storing, handling, analyzing and deploying any kind of referenced geographic information in order to solve complex management and planning problems.

MICRODEM is a freeware microcomputer mapping program written by Professor Peter Guth of the Oceanography Department, U.S. Naval Academy. MICRODEM displays and merges digital elevation models, satellite imagery, scanned maps, vector map data, and GIS databases. It requires a 64 bit version of Windows; an older version, which is not being updated, runs on 32 bit operating systems. You may freely use MICRODEM with no restrictions.

SAGA - System for Automated Geoscientific Analyses - is a Geographic Information System (GIS) software with immense capabilities for geodata processing and analysis. SAGA is programmed in the object oriented C++ language and supports the implementation of new functions with a very effective Application Programming Interface (API). Functions are organised as modules in framework independent Module Libraries and can be accessed via SAGA’s Graphical User Interface (GUI) or various scripting environments (shell scripts, Python, R, ...). »

uDig is a GIS software program produced by a community led by Canadian-based consulting company Refractions Research. It is based on the Eclipse platform and features full layered open source GIS. It is written in Java and released under GNU Lesser General Public License.

Supergeo Technologies Inc. is global leading GIS software & total solution provider. With series GIS products covering from desktop, mobile, server to developer SDK, SuperGIS has been utilized more than 100 different countries.

Mapline is the simplest mapping software on the planet! Be empowered with map visualizations from Excel spreadsheet data to optimize logistics, enhance market planning, identify growth opportunities, or mitigate market risks. Create your first map now!

MapWindow is a fully free and open source geographic information system project. It includes an open source programming component, MapWinGIS ActiveX, and an extensible desktop application that supports plug-ins written in .NET (C# and VB.NET). The most recent effort, MapWindow 6, includes a fully C# programming library that is intended to serve as an alternative to ESRIs ArcObjects platform.

MapInfo Professional is a powerful, functionally rich desktop mapping application from Pitney Bowes MapInfo, designed to enable organisations to solve business problems that have a geographical element.

Beautiful, User Friendly online mapping software that scales to big data.