JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
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Please be noted that Page Tab apps are not supported on mobile devices by Facebook's Platform: https://developers.facebook.com/bugs/435173473172584/
A workaround for now would be to use third party websites that offer a mobile version for tabs. You can also your page direct URL as well. Please check the following guide and look for (FAQ - 1. The page tab does not appear on mobile devices?) section: http://www.jotform.com/help/82-Adding-Form-to-Facebook-Custom-iFrame-App
For Facebook page, you might like to take a look at my colleague's solution on this thread in order to view your form on mobile device.
Feel free to contact us if you have any other questions.