Recently Wordfence announced a super-cool password auditing feature that cross-checks the user passwords on a site against a huge database of passwords and determines how easy would it be to crack the password. The feature is limited to Wordfence premium users. (http://www.wordfence.com/blog/2015/04/wordfence-announces-password-auditing/)
My question is that is there a free alternative that does something similar? I understand nothing can compare the passwords with a password database of that size, but there must be a few plugins that would be focussed on user passwords for WordPress, right? My end goal is to ensure all my users are using strong passwords but because I deal with users who aren't very versed with technology, I don't want to make their experience on the WordPress admin any cumbersome.
Additionally: is there a plugin that can, every n number of days, force a user to change the password upon login?