I have to give webappers credit for this one ... but these videos are quite useful for anyone creating some intro video for an app - or to show of your app. Ifind the green screen smartphone videos interesting and it might need some advanced video chops to pull them off - but if you have time and no money that's an option.

Pexels Videos - Free for Commercial Use
Pexels is a huge platform for free stock photos. Many designers and bloggers use it every day to find photos for their personal and commerical projects. No