IDEAS

CPU:

 - fake6502.c (Public domain)
 - https://github.com/bzotto/MCS6502 (MIT)

Sound: 

 - https://github.com/meenie/band.js (MIT)
 - https://github.com/daitangio/sid-arduino-lib (unlicensed? Platform: arduino)

Tutorial series:

 - https://www.youtube.com/watch?v=qJgsuQoy9bc&list=PLLwK93hM93Z13TRzPx9JqTIn33feefl37

PETSCII:

 - https://github.com/mobluse/x16-petscii2utf8
 - http://viznut.fi/unscii/ (SDL source)
 - https://dflund.se/~triad/krad/recode/pet_unicode.txt
 - https://dflund.se/~triad/krad/recode/petscii_c64en_uc.txt
 - https://style64.org/petscii/

BASIC:

 - https://github.com/mist64/cbmbasic

KERNAL:

 - https://sta.c64.org/cbm64krnfunc.html
 - https://www.pagetable.com/c64ref/c64disasm/ - documented dissassembly

GPL stuff:

 - https://github.com/MEGA65/open-roms
 - https://github.com/lgblgblgb/xemu