The Collaborative International Dictionary of English, CIDE for short, was derived from the 1913 Webster's Dictionary and has been supplemented with some of the definitions from WordNet. It is being proof-read and supplemented by volunteers from around the world.
This electronic dictionary is also made available as a potential starting point for development of a modern comprehensive encyclopedic dictionary, to be accessible freely on the Internet, and developed by the efforts of all individuals willing to help build a large and freely available knowledge base.
The original(?) version of the dictionary is maintained by a non-profit organization called World Soul. There are several derivative versions of this dictionary on the Internet, in some cases reformatted or provided with an interface:
Primary source: README.dictionary from GCIDE.