Great Britain Historical Geographical Information System (GBHGIS)
Other on-line projects
The Great Britain Historical GIS and many other projects in the field are affiliated to the Electronic Cultural Atlas Initiative (ECAI).
ECAI's core technology is Timemap, developed at the University of Sydney.
Most large projects have focused on demographic statistics, and on mapping the boundaries of reporting units. The GB Historical GIS also includes a large collection of scanned and geo-referenced historic maps. Another major on-line resource taking this approach is the David Rumsey Map Collection
The Historical Atlas of Canada On-Line Learning Project is not a true GIS, but demonstrates an interesting approach to on-line mapping.
Please let us know about other on-line historical GIS systems you think should be listed here.