Termux

Ready to go. Termux works directly with no rooting or setup required. At first start a minimal base system is installed automatically - you decide what to do next.

Powerful. Combine the flexibility and power of command-line tools - monitor multiple remote servers over SSH by tailing log files in tmux, sync dotfiles with git and encrypt secrets with gpg.

Feature packed. Take your pick between bash or zsh and nano or vim. Grep through your SMS inbox and use curl to upload backups of your contact list into the cloud.

Customizable. Install what you want through the Apt package management system known from Debian and Ubuntu GNU/Linux, which also takes care of keeping installed packages updated.

Explore. Have you ever sat on a bus and thought about exactly which arguments tar accepts? Packages available in Termux are the same as those on Mac and Linux - install man pages on your phone and read them in one session while experimenting with them in another.

Batteries included. Can you imagine a more powerful yet elegant pocket calculator than a readline-powered python console? Up-to-date versions of perl, python, ruby and node.js are all available.

Scale up. Connect a bluetooth keyboard and hook up your device to an external display if you need to - Termux supports keyboard shortcuts and has full mouse support.

Develop. Develop by compiling C files with clang or gcc and build your own projects with makefiles or cmake. Both gdb and strace are available if you get stuck and need to debug.