Doesn't FreeDNS deactivate your account if you don't log into their website for a couple of months, just like DynDNS did?

No, it's Dyn's and No-IP's thing.

From FreeDNS news page[1]:

"2012-03-29 18:20:33, 2 years ago: Free accounts not accessed at least once every 6 months will be considered dormant and unloaded from memory."

What does "dormant" mean here? Do they delete your DNS records? It might not be as draconian as what DynDNS was doing, but certainly a barrier you should consider.

[1]: http://freedns.afraid.org/news/

Here's an email I got from FreeDNS last year:

Your account at freedns.afraid.org has not been visited in at least 5 1/2 months.

User: Xxxxx Xxxxx (xxxxxxx) Last visited: 2013-09-21 (169 days ago)

Unless you visit the site anytime in the next 2 weeks, your account will be considered dormant. "Dormant" consists of unloading any stale DNS records from memory which you may have set up in the past.

This stale entries optimization will free up several gigabytes of memory, making it available for active users. This will allow a DNS server to do a cold configuration boot, and load in new zones in a fraction of the time and space.

Users supporting freedns.afraid.org with a premium plan of any kind (even the smallest) will not be affected.

What does "not accessed" mean? One could write a script that would log in every month or so, click around (very carefully of course ;) ) and logout. How would they know the difference?

As a matter of fact, that's what I was doing to bypass DynDNS limitations: running a PhantomJS script via cron once every week to login, click around and logout. But it is a tiny hassle anyway. Much better to stick around with a service that does not have these annoyances.

And that's just what I did with https://github.com/kopf/dyndns-autologin . A few months later, they discontinued the free service altogether.

Somewhat sadly, it was my github project that seemed at times to garner the most interest from outside, even though it was just a shoddy python script thrown together in a 10 minute cigarette break at work.