Fontra Pak (unofficial snap)

Fontra is an open-source, browser-based, cross-platform, variable-first
font editor.

It is developed by Black [Foundry] and Just van Rossum
with support from Google Fonts

Fontra extends the boundaries of what current font editors
can do. Originally developed to make the design and production of large
CJK fonts more efficient, Fontra provides deeper integration of
variable font technology and improved usability of variable
components as design elements.