These are Gargoyle's "custom" fonts.

Gargoyle Serif is a renamed Charis SIL, and Gargoyle Mono is a renamed Go Mono.
By giving them Gargoyle-specific names, they can be installed system-wide
without clashing with any other fonts, allowing Gargoyle to use them as its
defaults.

Earlier versions of Gargoyle could be built with fonts embedded so that it could
be run without the user having to install fonts. However, many fonts are
licensed under the SIL Open Font License, which is not compatible with the GPL,
which is what Gargoyle is licensed under. As a result, the number of possible
bundled (and therefore "default") fonts was vastly reduced. Specifically, Charis
SIL, which would have been the ideal successor to Bitstream Charter, is licensed
under the OFL, so for several years it was replaced with Noto Serif.

While there is nothing wrong with Noto Serif, it makes Gargoyle look different
than its original incarnation, so to allow Charis SIL to be set as the default,
font bundling was removed. To compensate for this, if the user does not specify
fonts, or if the specified fonts cannot be found, Gargoyle will try to load the
font files directly from two locations: a system-specific data directory (e.g.
/usr/lib/gargoyle/fonts), and, failing that, the current directory (Unix) or the
directory containing the Gargoyle executable (Windows).

This also includes GNU Unifont which is used as a fallback for glyphs which
don't exist in the user's preferred font. Unlike the Gargoyle fonts, this is not
meant to be installed system-wide. Instead, it is installed in a known location
and Gargoyle directly loads it, as opposed to using the system's native font
loading mechanism.

The licenses for these fonts are available in the top-level "licenses" directory.