Enthusiasts from the OpenCE Ports project have released an unofficial port of Halo: Combat Evolved for Android, based on the decompilation of the original Xbox version of the game.
According to the authors, the port includes the entire story campaign, and multiplayer support is also announced: you can play online or with four players on one device with a split screen, connecting a separate gamepad to each participant.
Touch controls and gyroscope aiming are also provided for smartphones, and the size and location of on-screen buttons can be customized.
To run it, you will need your own Halo: Combat Evolved image for the original Xbox.