Macros to Change Text and Mathematics fonts in TeX: 45
Beautiful Variants The macros are written for plain TeX and may
be used with other packages like AmSTeX, eplain, etc. They also
work with XeTeX. The macros allow users to change the fonts
(for both text and mathematics) in their TeX document with only
one statement. The fonts may be used readily at various
predefined sizes. All the fonts called by these macro files are
free and are included in current MiKTeX and TeX Live
distributions.

Homepage:
https://ctan.org/pkg/font-change
