Maybe once or twice I used it on Android too.
Not much.
Android is also Linux.
But I know that not every project support Android.
And some projects support only certain hardwares. For example AMD or Nvidia video cards.
Currently I do not have a separate Boinc account, but I have accounts with various Boinc projects.
For example the Milkyway@Home project.
I used it with Windows and with Mac PCs and laptops so far.
There's not really a separate BOINC account but I think all the accounts for the individual projects are linked for statistics purposes if you use the same e-mail address.