When Donald Knuth was working on his second volume of The Art of Computer Programming, he was shocked by the poor quality of the photoset galley proofs he got back from the printers. In an effort to regain the typographic control afforded by hot metal, and to guarantee standardized results across different types of output devices, he developed the TeX computer typesetting system. Part of TeX included the METAFONT language, which described fonts in terms of mathematically defined strokes, which generated bitmaps on the fly. This was an important step towards the outline fonts we use today.
Adobe Optical Sizes
Adobe experimented with a format called Multiple Master, which allowed the designer to generate variations of a typeface by changing the values of different axes. EAch axis controlled elements like weight, optical size, serif/sans-serif, etc. It proved too complicated for most people to deal with and was abandoned, but today Adobe offers their pro fonts in several optical variations. In so doing, they reclaim some of the subtlety that was lost in the transition to photosetters and digital type.
The Fell Types
Imported to England by Doctor John Fell in late 1600s for use at the Oxford University Press, these Dutch typefaces have been the subject of several revivals, which have aimed to keep the roughness of the original worn letterforms as opposed to interpreting them as modern fonts. Two notable Fell revivals are those of Igino Marini and Hoefler & Frere-Jones.