Emulation/Xbox

About the Xbox
The original Xbox is notoriously difficult to emulate. The emulation community once commonly underestimated the difficulty of emulating the Xbox due to its similarities with a PC. However, the Xbox is notably different than a standard PC in a number of ways.

Official
The Xbox 360 line, Xbox One line, and Xbox Series line all use emulation to offer backwards compatibility with Xbox games. While not all Xbox games are supported through this lineup, many are, and for these games this option is by far the easiest way to emulate them.

Wikipedia maintains a List of backward-compatible games for Xbox One and Series X, as well as a List of Xbox games compatible with Xbox 360.

CXBX Reloaded
A more current version of CXBX with somewhat higher capability than the original.

CXBX also aims to emulate Sega Chihiro arcade hardware, which is itself derivative of the Xbox.

CXBX
Among the first Xbox emulators, based on high level emulation. Capable of running homebrew. Limited compatibility.

Dxbx
A now discontinued fork of Dxbx written in Delphi object Pascal. It contained some unique features that other members of the family lack, including a symbol scanning engine.

XQEMU
A low level open source and portable emulator.

Very computationally demanding and requires numerous files to be dumped from a system to operate.

Other

 * Xeon - Early emulator focused on emulating Halo specifically.