1. Send them a Surface Hub or equivalent device.
2. Use something similar to ProctorTrack[1] to ensure that they're not using unauthorized programs, etc.
3. Anonymize their voice with i/o software.
[1] http://www.proctortrack.com/
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That being said, some companies actively discriminate, ala "culture fit." You can't anonymize culture without being devoid of it. Culture, for better or for worse can predict race/ethnicity/age/gender/nationality/etc in many cases as well.
What you could do, I guess, is so something similar to the Common App and have them answer a ton of short answer questions.
It's a difficult process because you have to clear out many things. Not just ordinary stuff like age or sex, but you can't have in-person or over-the-phone interviews because that instantly de-anonymizes the applicant.
Having said that, there are many companies that are trying to find such a process that keeps the applicant anonymous in an effort to increase diversity. It's still very early and nobody (I don't think) has found a process that works effectively yet.
Disclaimer: I don't work for Bytemark but have been a happy customer for many years
I can see how possibly in some companies this could be achieved but it seems like it would be for a job where you are just a number not a person - YMMV I guess.
https://medium.com/@jongold/meet-hiremyfriend-a-new-product-...