The Work Item Field History is OSS and available on Github.
UPDATE 10 August 2015 (220.127.116.11)
UPDATE 27 April 2015 (18.104.22.168)
UPDATE 02 April 2015 (22.214.171.124)
UPDATE 14 October 2014 (126.96.36.199)
UPDATE 20 August 2014 (188.8.131.52)
UPDATE 29 July 2014 (184.108.40.206)
The Work Item Field History for VS 2013 audits a specific field of a work item, showing only the revisions in which its value was changed.
This tool will be installed on Team Explorer below Work Items.
After this, type Work Item ID or search Work Item on Browse (...) and click on "Show Revision(s)" button.
Use Browse Button (...) and return Work Item ID
Use Combobox to filter specific field
The tool will show only revisions that the specific field was changed.