Box64 has the narrower scope of being the fastest possible x86-64 to {ARM64, RISC-V} userspace emulator for typical applications like games. QEMU is focused on

Box64 has the narrower scope of being the fastest possible x86-64 to {ARM64, RISC-V} userspace emulator for typical applications like games. QEMU is focused on both system and application level emulation across all sorts of architectures and use cases, with a focus on absolute accuracy where possible.