Yeah, it's a bit strange seeing this described as if it's a new thing.

1982: Knuth's paper "The concept of a meta-font" is published.

1991: Adobe's "Multiple Master" fonts are introduced.

1994: Apple's TrueType GX is introduced. (Later "Apple Advanced Typography".)

2016: OpenType "variable fonts".

Maybe "variable fonts" are better than their predecessors? It's hard to tell. But it's strange for the predecessors not to be acknowledged at all.

Much more information about OpenType's "variable fonts" can be found at https://medium.com/variable-fonts/https-medium-com-tiro-intr... -- discussed on HN at https://news.ycombinator.com/item?id=12501665 . (That article does mention TrueType GX and Adobe multiple masters, but not Metafont.)

Did Knuth touch on the ability to morph between different designs of a font, or was it simply the ability to do fonts as sets of curves so that they could be resized?

Edit: never mind, I looked up the original paper and find a good description in just the first paragraph. He definitely had variations of the letters in mind.

Metafont has never found wide adoption, because to be a triple threat of typeface designer, mathematician, and software developer, you basically have to be a tenured stanford professor or their grad student to have enough time to learn everything well enough to make useful type.

And even then, the typefaces made with metafont are often very poor designs compared to those draw in a GUI in a 'dumbfont' format.

Adobe Multiple Master, then TrueType GX, and now OpenType Variations, are a 'best of both worlds' compromise; the drawing quality of visually crafted outlines, and the continuous-space-type-family-in-1-file typographic flexibility of metafont.