I recently came across this handy app called Termux. It's a nifty terminal emulator for your phone! Very useful if you wish to connect to your Linux desktops or servers using ssh or scp to download files or to edit files. It is available on the Google Play and F-Droid stores. You might be sceptical given the limitations of the Android on-screen keyboard, but they've neatly overcome this by providing volume down and up button key combinations as well as an extra row on the on-screen keyboard.
Long pressing anywhere on the terminal screen furthermore provides you with a context menu allowing you to Copy and Paste, Share a transcript of the session with other apps, kill the process and display Help among others. Swiping from the left edge of the screen reveals a navigation drawer for managing terminal sessions and to activate the on-screen keyboard.
The combinations of commands accessible by the up/down button and touch keyboard combinations are adequate do most tasks you would normally do on a keyboard on a linux desktop. The extra row of keys are also user configurable. There is a Text Input mode to take advantage of the advanced features of the on-screen keyboard (such as AutoCorrect, Predictive text, and swipe typing). The text input mode is accessed by swiping the extra key row to the left. I found it very awkward using Text Input mode for entering commands, but it should be useful when editing files.
To make the terminal emulator even more useful you can install the Termux:API app and get access to some of your mobiles functionality as command line programs. To use it you also need to install the termux-api package:
pkg install termux-api
This gives you access to information about sensors, your device's camera and media storage. For a full list visit the Termux wiki.