Arduino hardware package for ATmega64, ATmega128, ATmega165, ATmega169, ATmega325, ATmega329, ATmega640, ATmega645, ATmega649, ATmega1280, ATmega1281, ATmega2560, ATmega2561, ATmega3250, ATmega3290, ATmega6450, ATmega6490, AT90CAN32, AT90CAN64 and AT90CAN128
Why do you think that https://github.com/feilipu/Arduino_FreeRTOS_Library is a good alternative to MegaCore