The website is there at https: as you say, but the relevant download page (accessed from Extras on his site) returns a 404.
Yes, but I'm trying to ensure https://cumuluswiki.org/a/Category:User_Contributions is comprehensive and has right links
EDIT: Just discovered he has an old site and a new site.
The old site https://oaktreewebs.co.uk/resources/index.php as referenced in this topic has no data and all the links go to 404.
The new site https://oaktreewebs.co.uk/templates.php says he is working on template pages, it does not link to the responsive pages he used to offer
I only downloaded the Cumulus 1.9 zip and that is on Wiki, I did not download his old MX zip, so have edited wiki to say go to his website while leaving link to this topic.