The Xbox is a console produced by Microsoft Corporation in 2001. Known originally as the DirectXbox, this console is notable for essentially being a PC, as a result of using components from both Intel and Nvidia, as well as being x86-based. It is the most powerful console of the 6th generation as a result.
The common misconception with the Xbox is that due to being x86-based, it should be easier to emulate. This couldn't be more wrong. While the x86 architecture itself is fairly well documented, it is HUGE, as well as the fact that the specific hardware components within the Xbox are not very well documented at all, especially the Nvidia components. This has meant that overall compatibility of emulators for Xbox have been extremely low, supporting only a handful of games.