- testing short code in various repls

- using qalculate! for complex calculation (think physical constants, unit mixing, trig), currency and unit conversion, simple symbolics

- ffmpeg. i have aliases for video compression, stripping audio, etc

- converting between file formats, imagemagick and pandoc

- untarring files, encrypting files, batch renaming

- sending files somewhere else via scp

- remote controlling computers

- it's possible to set up a vnc server and a full gui desktop environment, for a highly portable system that gets you the same program and file setup on any computer supporting a vnc client.

Once you build up a collection of aliases / shell functions it can be very powerful even with a small virtual keyboard. The fish shell is also a great qol addition.

How do you get ffmpeg and other goodies you mentioned? Is there some software repo termux maintains? Is downloading software that way reasonably "safe"? I've used Termux before but never considered these things...

Termux doesn't get special privileges unless you root your device. It can't go messing with your phone data unless you granted it permission to do so (but even then it doesn't have access to everything). It's no worse than any other Android app IMHO.