I have been working for a couple months on a new website/app idea. I have finished the design process but now I need to create a user friendly demo to show to people to gather some data/feedback and eventually demo it to investors. I am looking for a good software to design the UI. I'd like to focus on how the buttons, links, labels, text-boxes work together, ignoring the content (it can remain static) Any suggestions? Thanks!
Take a look at Adobe XD. It is a drag-n-drop prototyping application for mobile apps and websites. It is intended for designers that have no programming experience, and it really is amazing how powerful it is for creating a professional prototype.
Adobe offers XD for free, so you can download it and do the tutorial. You'll see how easy it is to make something impressive in ten minutes.
I recently worked on a project where the designers used Invision. So I didn't create the designs, but I was able to comment on the designs and make change requests. The designers were not developers and only did interface design and mockups with invision.
So you could do a mockup without programming anything and present the basic app to investors.