Diag64
http://tech.guitarsite.de/c64_diag_dt_cart.html#DIAG64cart
https://github.com/svenpetersen1965/Diag64cart/tree/main/Firmware/bin
https://www.pcbway.com/project/shareproject/W160781ASB18_Gerber_1790f9c8.html https://www.pcbway.com/project/shareproject/Commodore_64_Expansion_Port_Cartridge_Project_Development_PCB_85ba470a.html https://www.pcbway.com/project/shareproject/OpenC64Cart_V2__8K_.html
https://www.pcbway.com/project/shareproject/C64_Magic_Desk_512k_Cartridge.html
diags:
http://blog.worldofjani.com/?p=164
cart creation
https://github.com/lvcabral/cart64-maker
https://diychris.com/how-to-create-a-c64-cartridge-from-a-prg-file/
roms: https://wowroms.com/en/roms/commodore-64/
to consider: https://www.pcbway.com/project/shareproject/Universal_C64_1MB_cartridge.html
various projects on pcbway: https://www.pcbway.com/project/shareproject/EasyFlash_1CR_cartridge_wide_sram_7bbb44b3.html http://www.skoe.de/easyflash/efintro/ https://www.pcbway.com/project/shareproject/EasyFlash_1CR_cartridge_narrow_sram_5056bf02.html https://www.pcbway.com/project/shareproject/EASYFLASH_CARTRIDGE3_PCB_V1_3.html https://www.pcbway.com/project/shareproject/Universal_C64_1MB_cartridge.html https://www.pcbway.com/project/shareproject/C64_Magic_Desk_512k_Cartridge.html https://www.pcbway.com/project/shareproject/_64kCart__Bank_Switching_Cartridge.html
https://www.hackup.net/2019/07/bank-switching-cartridges/
https://www.pcbway.com/project/shareproject/C64_Magic_Desk_512k_Cartridge.html https://www.pcbway.com/project/shareproject/Magic_Desk_2_for_Commodore_64_62898d63.html https://www.pcbway.com/project/projectsearch?q=kung+fu+flash&t=1 https://www.pcbway.com/project/shareproject/KungFuFlash_Cartridge_rev_2.html https://www.pcbway.com/project/shareproject/UC1___Ultimate_Cartridge_1.html https://www.pcbway.com/project/shareproject/Nano_SwinSID_for_Commodore_1.html https://www.pcbway.com/project/shareproject/W51851ASY54_OneDiagBoard_rev_A.html