There must be something wrong with the redirect of www links to the non-www link for this domain. There’s a bunch of links on commontk’s website that have the broken www version.
I don’t own the commontk.org domain, and I don’t remember for sure who does. Maybe Kitware? (@jcfr do you know?) However I went ahead and fixed the repository homepage link and also the CTK code so most things won’t break. Would be good to fix the redirect to fix any lingering links.