Prototype for new product

I'm looking for a prototype for a new product and am open to suggestions for the features. The main purpose for the prototype is to test functionality, so any ideas you have are welcomed. The prototype I'm looking for is a digital one. I have a basic list of features in mind but am open to any suggestions you may have that would make the prototype better. The successful freelancer will be able to demonstrate excellent knowledge of digital prototyping in order to create a successful prototype which meets my needs and remains flexible based on potential changes.