The CM93 data seems to come from C-Map. They only have NT+, MAX, and MAX Pro today so maybe CM93 data is really free?
It was the most widely distributed chart package due to lack of encryption, or encryption that was easily cracked (I can't recall
which). It's definitely still licensed/owned, not free to distribute, etc.
Almost every anchorage will have someone that has "CM93's", most of which are old, some are really old/broken (lateral markers missing from inland waterways and other oddities.)
If someone is after freebies, I think there's better options out there that can even be used on some plotters with a bit of work (I won't name them here).