We do performance reviews, order forms, etc all through formcentral. This is going to really hurt us as well.
Do any of the listed alternatives allow a user to fill out a form off-line like a .pdf form with a submit button (as formcentral did)? We have users that cannot get to websites but can work on a .pdf form.
And not formstack - that pricing model is absurd.
I can't speak to the functionality provided by the alternative solutions listed in the FAQ: End of support | Adobe FormsCentral.
But, can you repurpose your forms as PDF forms for use with Adobe Acrobat. Information about that is discussed in the FAQ as well.