The extrafontdb R package was created and maintained by Winston Chang on github for more than 13 years with a first commit on github the 25th of May 2012. The previous commit history of the package can be found here. The responsibilities and attention of Winston Chang are on things quite far away from fontcm, extrafont, extrafontdb and Rttf2pt1 these days. I volunteered to maintain fontcm and extrafontdb (read here) in addition to extrafont and Rttf2pt1.
The following text almost exactly the original readme from Winston Chang repository on github, only some links were updated and badges and doi added.
https://doi.org/10.32614/CRAN.package.extrafontdb
The extrafontdb package is meant to be used with the extrafont package. The extrafont package contains the code to install and use fonts, while the extrafontdb package contains the font database. (When initially installed, this package is essentially empty, except for some directories; the database itself is created by the extrafont package).
The code and the database are separated into two packages because each time that the package containing the database is re-installed, the database gets deleted. By putting the database in a separate package, it is possible to update the code package without deleting the database and having to re-import the fonts.
Re-installing this package will re-initialize the font database, and all font will need to be re-imported.
See https://github.com/wch/extrafont for more information.