I wrote a small application a while back to allow a team to figure out what their average salary was without exposing individual salaries. Seems relevant.

https://are-we-being-underpaid.herokuapp.com/

It generates unique URLS for each participant and stores almost nothing on the server. Only a party that was actively monitoring web traffic has enough information to divine someone's salary. No tracking of emails, salaries, etc.

Source code here https://github.com/pipermerriam/am-i-underpaid