Ubuntu touch, an alternative control system (OS) for phones and tablets. An interesting idea, but …..
The kernel used is that of Ubuntu 16.04. This was EOL for several weeks (no more updates) when it was tested the OS. Various applications, such as FireFox, are also not available, while it is available in other mobile operating systems.
From a security point of view (old kernel) and the lack of large applications, I have stopped exploring it further.
Let us know in the response which alternative mobile OS you want a review or which you have tested.