JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
JotForm forms can easily be used in any device with a web browser that has an active internet connection.
Your users can easily fill out the form by using the form's direct link, you can get the link under "Publish"->"Link"
Now these forms don't need to be on a mobile app, you can make them mobile responsive by following this guide: https://www.jotform.com/help/322-How-to-make-mobile-friendly-forms-on-JotForm
This allows the form's layout to automatically adjust best fitting for the screen display of the device where it is being viewed.
You can also embed your form on a website page, here's a guide that you can follow: https://www.jotform.com/help/34-Adding-a-form-to-a-web-page.
If you want it to be on an Android app or iOS app, then you need to first create your own mobile app, that app should allow you to embed the form using its embed codes that we have. The app you should be creating should also NOT block JotForm's resources which will also lead to your form to not function fully.
I hope that helps.