https://mcudude.github.io/MightyCore/package_MCUdude_MightyCore_index.json
https://mcudude.github.io/MiniCore/package_MCUdude_MiniCore_index.json
https://mcudude.github.io/MegaCore/package_MCUdude_MegaCore_index.json
https://raw.githubusercontent.com/damellis/attiny/ide-1.6.x-boards-manager/package_damellis_attiny_index.json
http://digistump.com/package_digistump_index.json
https://github.com/stm32duino/BoardManagerFiles/raw/main/package_stmicroelectronics_index.json