Android - Emacs on Android
I have ported Emacs to Android. (Google Play, Github)
It doesn't draw UI like Linux X11 version, but uses modified Android Terminal Emulator.
From what I understand, it is not possible (at the time of writing this), since almost all the dependencies that are required for emacs to run do not exist on the android system. then, even if you got all the dependencies to compile for ARM and android kernel, it would take longer to start up emacs then it would to ssh in to another machine that has emacs available.
If you want to try, you can look at this site that explains what you need to do to compile linux binaries for the Android devices. And here is how you build emacs.
If you have Lollipop or above, Termux is an terminal emulator and linux environment where you can install Emacs via
apt update; apt install emacs. Or checkout this nice post on how to do get it running.
I have Emacs running in my CyanogenMod tablet using this method.