The Vision of Britain site is the main public face of the Great Britain Historical GIS, but we are also supplying boundary data and other resources to online partners:
The National Library of Wales — Welsh Tithe Maps
This project, funded by the Heritage Lottery Fund, is conserving over a thousand Welsh tithe maps but also using crowd-sourcing to create a place-name index. Each map generally covers a single parish, so our boundaries provide an integrating framework.
http://cynefin.archiveswales.org.uk/en/tithe-maps/

The National Library of Scotland — Scottish parish boundaries
The NLS are another of our partners in the GB1900 project, and they are also using our boundaries, this time for Scotland:
http://maps.nls.uk/geo/boundaries/

King’s College London — Mapping the Medieval Countryside
This is a major research project dedicated to making the medieval inquisitions post mortem, listings of people’s property when they died, more widely available and accessible through a digital edition. It was funded by the Arts and Humanities Research Council. There are no comprehensive maps of actual medieval boundaries, so the site uses our early nineteenth century boundaries to help provide context.
https://www.inquisitionspostmortem.ac.uk/browse/places/
English Place Names Society — Historical Gazetteer of England’s Place-Names
This site is a bit different, as rather than using our boundaries it uses our web map server to supply historical base maps; the way this works means the base mapping comes straight from our server to their users’ web browsers. For example:
http://placenames.org.uk/browse/mads/epns-deep-39-b-subparish-000058

This site was created by the Jisc-funded DEEP project (Digital Exposure of England’s Place-names), and we also assisted them by supplying point coordinates for each parish, computed from our digital parish boundaries. The main sources for the gazetteer are the county surveys carried out by the Survey of English Place Names, started in 1923, but don’t try looking for places in Hampshire — they have not started that survey yet.
We have made these resources available to these non-commercial UK-based projects free of charge. However, our main source of income is licensing digital boundary data for commercial and non-UK use. For details, contact us at gbhgis@port.ac.uk.
Humphrey Southall