Darcelf/Alg5 has released a new emulator for Xbox.

Xzx81 is an xbox port of Xz81, a zx81 emulator.

"The Sinclair ZX81 home computer, released by Sinclair Research in 1981, was the followup to the company's ZX80. The case was black, with a membrane keyboard; the machine's distinctive appearance was the work of industrial designer Rick $#@!inson. Video output, as in the ZX80, was to a television set, and saving and loading programs was via an ordinary home audio tape recorder to magnetic audio tapes."

heres the info:

The screen, keyboard, tape reader and sound(!) are emulated.
The keyboard is emulated using a virtual keyboard.
The sound emulate a sound addon called Bi-Pak Zon X-81 that was using an AY chipset (much like the Atari ST, Amstrad CPC...)

To Do:
* Joystick emulation ?
* Add a menu to select some options (reset, type of sound addon ...)

More info here --> http://www.darcelf.tk/