Requires mouse & keyboard
This started off as: 'I wonder if I can get the ZX Spectrum font into pico-8?'
I then realised that 16 chars per line isn't particularly practical, and wrote a font editor.
Features:

edit, save, export fonts for use in pico-8
change width & height of font characters
adjust width per character
cut, copy, paste, undo, nudge
8 internal save slots
exports a .txt file to desktop that will run in pico-8 to use the font in other projects
uses ZX Spectrum font as initial template

Limitations:

saveexport won't work in browser
only edits the main 96 characters (i.e. Spectrum font)
no undo on the file screen!
fonts are saved internally to cart rom on exiting the file screen, cart must be saved to keep changes.
can't load external fonts
exported code is verbose, but I wanted to keep things readable.