Map resources is primarily for benchmarking tools and projects that already exist in the domain.

Wikimedia tools & technologies

Map resources on Wikimedia Commons
The Graphic Lab Creating maps on request
Map guidelines SVG toolboxes, common style & guideline (2 schools), expanding
OSM-Gadget
WikiMiniAtlas
Geohack

OpenStreetMap & related

Georeferencer that is being used in relation to the Old Maps Online project and the British Library Maps project
MapWarper It's a free to use, open source map warper / map georectifier. This project is supported by Topomancy and the New York Public Library. http://maps.nypl.org/, http://warp.worldmap.harvard.edu/
Sharemap calibrating tool

The list is not complete by any means. It's category for links that have come up in various occasions. Please add your favourites to the list.

TileMill A map design environment from MapBox. GitHub
Gunn map 2 A thematic world map creator: Countries, color ramps, data import, SVG export. Used in Wikimedia.
Sharemap.org
Crunchtime GitHub A time-enabled OSM visualization, by Nick Doiron from Chicago Hack Weekend. by way of Jeff Meyer on OHM list.

Old maps online
WatWasWaar: WatWasWaar.nl is a national platform for disclosing historical-geographical information on the Netherlands to a wider audience. The site has several search vectors: Where (location), what (typology), when (time) and which (institute). The site has a nice interface to find things using these vectors. The site doesn't seem to have any user contributed content and the software doesn't seem to be open source. Site is operated by a consortium.
Global World History ATlas A project by Jeff Meyer, collecting together maps resources from all around the world for easy reuse especially in educational environments.
Historical Helsinki A prototype for displaying historical map layers on a map/aerial image. By Janne Aukia GitHub
Denmark seen from the air The Danish Royal Library's service for aerial images of Denmark from 1913 to 2009.
Kartenportal.ch Swiss map reference portal.
Historisk Atlas is a map portal for historical maps from a joint effort of cultural actors in Denmark, lead by the City museum of Odense. New HTML5 beta
Maps of the National Library of Scotland

Pleiades is a community-built gazetteer and graph of ancient places. It gives scholars, students and enthusiasts worldwide the ability to use, create, share, and map historical geographic information about the ancient world. It associates names and locations in time and provides structured information about the quality and provenance of these entities. Pleiades is a joint project of the Ancient World Mapping Center, the Stoa Consortium, and the Institute for the Study of the Ancient World.
Pelagios
Limes
Finnish Spatio-Temporal Ontology (SAPO) is an ontology time series of Finnish municipalities over the time interval 1865–2010. Modeling these changes can be done using ontology time-series that represents knowledge about changes (e.g. merges, splits) in historical regions (e.g. cities, counties) and a method to help creating geospatial ontology time-series. Created as a part of the FinnONTO at Computing Research Group (SeCo)