What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
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.
I'm not quite sure what you meant by custom matrix, could you please provide us more information about this?
You can see our Matrix field under the "Survey Fields" section.
You can also perform calculations based on the inputs in your matrix field. Here's a guide about it: https://www.jotform.com/help/343-How-to-Perform-Form-Calculation-in-the-Matrix-Field
Let us know if I misunderstood your concern.