Android has (through FDroid, as Google Play Store no longer permits it) Termux, The Only App Which Does Not Specifically and Precisely Suck[tm] (though as before, Einkbro is increasingly stiff competition).
Termux offers an arguably rich Linux userland, with over 2,500 packages (2,581 listed as I write this). That's still a small fraction of the total number of Debian packages, which now exceeds 57,000, but the tools which are available are a highly useful set and includes numerous scripting languages (Perl, Python, Ruby, Node.js, etc.) and compilers, along with several repositories associated with those tools. All told, Termux is far more than a toy.
But ...
... it's still hampered by numerous Android limitations:
- No root access unless your device is rootable (and rooted).
- No multi-user capabilities or security.
- Limited to the default Android filesystem limitations (including being locked out of most of the filesystem), and limited filesystem permissions capabilities.
- Subject to Android's process-management and process-reaping "features", which mean your shell session(s) may be killed off at any time.
- Limited on-board keyboard support. Even with an external bluetooth keyboard there are quirks and issues.
I can do, and do do quite a bit with the system. It remains limited and crippled in numerous ways though I can often avoid the sharpest of edges.
There's no full-fledged equivalent on iOS, and many years of attempting to provide even a fraction of Termux's capabilities (through ISH) seems to be running into even steeper headwinds than Termux has had to deal with.