Well by gosh, I am old enough to remember Adobe Multiple Masters…
https://blog.typekit.com/2014/07/30/the-adobe-originals-silv...
…a technology which went absolutely nowhere.
Makes me glad to see Helvetica is now available as variable, as well as a non-trivial number of open-source fonts.
https://fonts.google.com/?vfonly=true&sort=popularity
(Still waiting for Roboto, though. Slab and mono are there, the main sans isn’t yet, which is too bad.)