Take a look at: Form Builder (Drag and Drop) + Form Server Validations for example of processing data from external forms.
But you would have to modify the Tasklist app for it to load forms from another source. Depending on your level of complexity, replacing the tasklist app is not overly complex. Just need to cover a few use cases.
See the link above as it goes through multiple scenarios, examples, and has diagrams and photos of working examples.