This is probably unrelated, but there is this Extension:
It records the number of times each post was read.
I haven't seen anything that records the number of people logging in and logging out of the site. I presume this means people who are logging in and logging out of the /Account/login.aspx page.
Something like this would probably need to be created from scratch, unless someone else has already created it. Generally people are not tracking logins & logouts though, so probably such code does not already exist (just a guess).