Is there a way to create reflowable ebooks without using Amazon technology?

Hi,

I am trying to create reflowable ebooks. The ebooks are in epub format and are in Arabic language.

That being said, epub is not supported on Kindle on iPhone. Also, I do not want to publish them on Amazon to be able to get the ebooks to reflowable.

Is it possible to convert epubs into a format using Calibre or Sigil that is reflowable on Kindle apps?

Thank you.