We would like to do a survey. We want to be able to track who has responded, so we can send out an email reminder. But at the same time we want privacy for the respondent, so we cannot tell who answered what. It is not sufficient that we promise to remove the link between the email address and the response.
I seem to remember that this problem has been solved in e-voting (i.e. we can tell you have voted, but not what you voted).
Is there survey software that can do this?
We will prefer free software.