* Some emulator do exists. The earlier attempts were just API translation layers that work a bit like wine: translate the function calls to native system APIs on windows. As time went, tricks and workarounds were piling up, especially as some games used lower level HW functionality (writing in registers, etc), which provided difficult to emulate, and game executables had to be patched, thus making the emulators a collection of special cases. Such emulators include Xenia, Cxbx (and derivatives such as shogun's version, dxbx, etc).
* More recently, efforts turned to low-level emulation, with complete emulation of the Xbox GPU, using a codebase derived from QEMU: XQEMU, and more recently XEMU (mborgeson's fork, focused on trying less-proven tricks and workarounds to maximize compatibility). Both are being developed in the open (XQEMU's development process might be slightly more open), and reverse-engineering is ongoing.
* Big names (among others) on the emulation scene: mborgeson, JayfoxRox, Espes, Shogun
* Bunnie Huang’s Hacking The Xbox was mentioned by another commenter, but 17 Mistakes Microsoft Made in the Xbox Security System is also an interesting read about working around the Xbox security mechanisms: https://xboxdevwiki.net/17_Mistakes_Microsoft_Made_in_the_Xb...
* Some emulator do exists. The earlier attempts were just API translation layers that work a bit like wine: translate the function calls to native system APIs on windows. As time went, tricks and workarounds were piling up, especially as some games used lower level HW functionality (writing in registers, etc), which provided difficult to emulate, and game executables had to be patched, thus making the emulators a collection of special cases. Such emulators include Xenia, Cxbx (and derivatives such as shogun's version, dxbx, etc).
* More recently, efforts turned to low-level emulation, with complete emulation of the Xbox GPU, using a codebase derived from QEMU: XQEMU, and more recently XEMU (mborgeson's fork, focused on trying less-proven tricks and workarounds to maximize compatibility). Both are being developed in the open (XQEMU's development process might be slightly more open), and reverse-engineering is ongoing.
* There is also an ongoing effort to port ReactOS to both the Xbox and XQEMU (probably using the official nvidia NV2A driver): https://reactos.org/wiki/Install_ReactOS_on_Xbox
* Big names (among others) on the emulation scene: mborgeson, JayfoxRox, Espes, Shogun
* Bunnie Huang’s Hacking The Xbox was mentioned by another commenter, but 17 Mistakes Microsoft Made in the Xbox Security System is also an interesting read about working around the Xbox security mechanisms: https://xboxdevwiki.net/17_Mistakes_Microsoft_Made_in_the_Xb...
* I cannot stress enough how https://xboxdevwiki.net/ is a great resource for information. Other links: https://xqemu.com/ https://github.com/xqemu/xqemu/ https://xemu.app/ https://github.com/mborgerson/xemu/wiki#content-top https://shogun3d-cxbx.blogspot.com/
* There is a big discord community, some rooms are bridged with IRC on freenode, I also bridged #xqemu on Matrix: https://xboxdevwiki.net/Main_Page/Header