XQEMU is an Xbox emulator that had started development relatively recently. The project is actually based off of QEMU, an open-source computer virtualizer. The thing that makes this emulator different from the other attempts at Xbox emulation is that XQEMU uses low-level emulation (since QEMU itself is a low-level emulator), while previous Xbox emulator attempts used high-level emulation. This comes with it's own benefits and downsides compared to high-level emulation, but it does allow for greater accuracy – and in turn – greater compatibility down the road.
XQEMU is at a very early stage right now. Quite a lot of games can run on it, but it's low-level, accuracy-focused, and there hasn't been much (if any) focus on speed, so games are very slow on it currently. There is some work being done to make it use KVM, which could significantly increase speed, but it's currently not recommended and Linux only.
You'll need a MCP-X boot rom, Xbox 1.0 compatible BIOS, and a HDD image with a dashboard, all in the main XQEMU directory. Then run:
qemu-system-xbox -cpu pentium3 -machine xbox,short_animation,bootrom=mcpx_1.0.bin -m 64 -drive file=xbox_harddisk.qcow2,index=0,media=disk,locked=on -drive index=1,media=cdrom,file=game.iso -bios complex_4627debug.bin -usb -device usb-hub,bus=usb-bus.0,port=3 -device usb-xbox-gamepad,bus=usb-bus.0,port=3.2
game.iso to the filenames of the boot rom, BIOS, and game ISO that you're running.