Existing software

From Dedupe

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TBC

Uniserv

I think Uniserv is one of the most successful players in the field of address cleansing and merging. As far as I know, their licence terms make you pay per "hit" or something like that.

Silversmith Refiner

This product was formerly commercial, now GPL. No longer maintained by original author. Based on MS Access, awk, agrep, and shell scripts. See archived web site for a detailed description: Silversmith Refiner (on the author's home computer, which is sometimes turned off).

Sources and reference materials generally useful for dedupe projects: refiner.tar.bz2

Unfortunately, in order to protect the formerly proprietary code, convoluted encryption and obsfucation schemes were applied to the scripts. It also has a license activation feature that needs to be removed/circumvented in order to get the full function.