Documents of Essex England Data Set (DEEDS) was founded in 1975 by Professor Michael Gervers to create a database of information culled from medieval English property exchange documents which would be of interest to social and economic historians. We now have an extensive ORACLE relational database containing some 300,000 records. Personal names, relationships, occupations, properties both tangible and intangible, places and, where available, dates, are easily accessible to the researcher. This is supplemented by a digitized map of the parishes and Hundreds of Essex which is used to plot information.

Our principal source is the Great Cartulary of the Order of the Hospital of St. John of Jerusalem in England, written in 1442. This has been augmented by the Feet of Fines for Essex from 1182-1307 and by selected entries from the Calendar of Inquisitions Post Mortem for the period with particular reference to Essex. There is also a supplementary database of information about tradespeople which has been gleaned from a number of smaller Essex cartularies.
http://www.utoronto.ca/deeds/research/research.html

I'm sure this will be valuable to many of us-