We are working on combining our products and pushing people toward owning all of them through the extension library so that people won't feel left with half a solution.
A form can be used to email, manipulate a database, update files, or do any number of other things. We had products to do those other things, but nothing to help you create the form itself. Form builder was created to fill that hole.
Now that the hole is filled we can concentrate on tighter integration. Form Builder is a v1 product, and v2 will certainly include more.