I'm sure someone has already requested this feature, but I'd like to add another vote.
It would be very helpful if the Forms had the ability to add a hidden (not displayed) field that could be prepopulated by either the creator of the form, or by whoever is embeding the form in a web page or platform. This way, information could easily be added to the Contact's entry that would identify which platform or product was used to fill out and submit a given form.
Thanks for the feedback. This has been requested and I'll make sure your vote is tracked as well. I personally think this is a great idea as currently our web UI only shows "Other App". This is a feature I've been asking for as well.