Any way to submit data at every page?

A multi-page form is NOT submitted until the final page is submitted. There is no partial data storage. The form isn't processed until the final page is submitted.

The purpose of multi-page forms is to break up long forms to make them less intimidating and to encourage users to complete the process. The longer the form, the less likely it is to be completed. Splitting the form into multiple pages makes the form seem a little less daunting.

Partially saving data is a privacy and transparency issue. Users don't expect information to be received and stored until the form is fully submitted and a confirmation action is displayed.

Not all abandoned forms are going to be accidental. Typically it's going to be because the user decided to not complete the form. Capturing partially filled out forms that a user may have purposely chosen NOT to submit because they decided against it at some point during the process is not something we agree with and not something we ever intend on implementing.

We do plan on implementing save and continue functionality but it will be done in a way that it is clear to the user what is happening and what it is going to do for situations where the user wants to complete the process but doesn't have time so they want to save their progress and continue at a later time.

Yea, it's definitely possible. You can do this using 2 different forms with the 2nd form optional. Just create 2 different forms. Then configure the first form to redirect to the page containing the second form for it's confirmation. You can then configure it to pass form field data via the query string to the page containing the second form. This can then pre-populate fields in the second form, including hidden fields.

What I described above can be done completely without code. You just use the URL Redirect option on the confirmation to redirect to the page containing the second form and the query string builder with the URL Redirect option to build your query string to pass form field data (ex. email=the@email.com)

Then you would configure your second form so that the fields you want to dynamically populate are configured to be allowed to be populated dynamically and set the parameter name for the fields via the Advanced tab so the parameter matches what you are using to pass the field value via the query string (if you are passing email=the@email.com in the query string then email is the parameter name).

You can read more on how to dynamically populate a field, including via the query string, here:

http://www.gravityhelp.com/documentation/page/Using_Dynamic_Population

Yea, if you are using AJAX it isn't going to be seamless. It would require a page refresh to redirect to the second form. I can't think of any solutions to this off the top of my head.

It might be possible via jQuery. There are hooks that Javascript hooks that are triggered at various points. You can read more in the Developer Documentation area here:

http://www.gravityhelp.com/documentation/page/Developer_Docs