This is about installing Emacs into an Android device. See GoogleAndroid for tips about using Emacs to develop Android applications.
A native Emacs on Android, without requiring root or special setup, can be installed in the Termux terminal emulator application by executing:
apt update && apt install emacs
For a Linux and Emacs environment in a chrooted loopback filesystem on a rooted tablet, see Running Emacs on an Android tablet. Android apps such as ConnectBot shell client and Hacker’s Keyboard (including Ctrl, etc. keys) can be used with Emacs in this way.
Besides running Emacs inside a true chroot, it’s also possible to get a running Emacs from a ready GNU/Linux distro package in an unrooted Android – as a faster solution compared to the native app option, which would require some work on adapting and recompiling Emacs against the Android environment.
This is possible with the GNURoot app. It allows to use a GNU/Linux distribution like Debian in an unrooted Android.
The GNURoot app does all this by means of a PTRACE container implemented by proot: interception of syscalls and “emulating” what should be done in the different Android and unprivileged environment (redirecting paths, faking the root user privileges, etc.).
It’s a pity that the source code for GNURoot seems not to be well documented, so it’s not easy to start hacking with it right away or at least learn how all the things have been compiled and put together from source.
This is by far the easiest and fastest way. It does not require uninstalling Android, and Emacs will run at normal speed. You could also use VNC if you need graphics.