Entware MIPS: https://www.asuswrt.eu/how-to-install-entware/
This version is for MIPS devices: RT-N16, RT-N66U/R, RT-AC66U/R

Entware ARM: https://www.asuswrt.eu/how-to-install-entware-arm/
This version is for ARM devices, like RT-AC56U, RT-AC68U, RT-AC87U