GeoNode!

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.

MapBox makes it easy to design beautiful custom maps, and fast to integrate them into websites and mobile applications using Open Street Map data.

OpenGeo provides support and services around GeoServer, OpenLayers, PostGIS, GeoWebCache, and GeoExt.The OpenGeo Suite brings together the OpenGeo Architecture into a single, easy-to-install integrated software package. By developing each individual component of the OpenGeo Suite individually, we ensure that the Suite integrates with existing systems—proprietary or open source. It is the fastest way to get your geospatial information on the web, leveraging the power of best-of-breed open source geospatial software. »

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

KeplerJs is a open source geosocial solution that lets users share favorite places and join discussions in real-time. It can be seen as a platform where users can interact with other open data platforms searching across OpenStreetMap, Geonames among other sources.

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.

Esri Geoportal Server is a free open source product that enables discovery and use of geospatial resources including datasets, rasters, and Web services.

The Géoclip interactive mapping solution is proposed by EMC3. Géoclip permits to publish online thematic atlas or territorial observatories. Géoclip allows you to build web mapping applications for cartographic representations of statistical data.

The Map Kit framework provides an interface for embedding maps directly into your own windows and views. This framework also provides support for annotating the map, adding overlays, and performing reverse-geocoding lookups to determine placemark information for a given map coordinate.

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

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.

What3words encodes geographic coordinates into 3 dictionary words (for example, the Statue of Liberty is located at planet.inches.most). what3words is different from other alphanumeric location systems and GPS coordinates in that it displays 3 words rather than long strings of numbers or letters. what3words has a website, apps for iOS and Android, as well as an API that enables bidirectional conversion of what3words address and latitude/longitude coordinates.Source: Wikipedia

MapET Spatial Feature Server is software that makes your geographic information (vector data) available to others in your organization and optionally anyone with an Internet connection. This is accomplished through web services, which allow a powerful server computer to receive and process requests for information sent by other devices. MapET Spatial Feature Server opens your GIS to devices that can connect to web services.

MapServer is an Open Source platform for publishing spatial data and interactive mapping applications to the web. Originally developed in the mid-1990’s at the University of Minnesota, MapServer is released under an MIT-style license, and runs on all major platforms (Windows, Linux, Mac OS X).