Images
For some time, when looking for images online for your app or site I have been going to Unsplash. As I come across more image sites that are noteworthy they will be added to this list.
Unsplash (https://unsplash.com) – is an amazing resource for beautiful, high-resolution and free photos
Moose (https://photos.icons8.com) – library of royalty free images and stock photos for personal and commercial use
Prexel (https://www.pexels.com) – Free stock photos you can use everywhere... Free for commercial use
Undraw (https://undraw.co) – really cool vector illustrations that has been created by Katerina Limpitsouni
Icons
Heroicons (https://github.com/tailwindlabs/heroicons) – is a free SVG icon set created by Steve Schoger. They're pre-optimized and easy to use directly in your HTML where you can customize them using Tailwind's color and sizing utilities.
Zondicons (http://www.zondicons.com/) – is another set of free premium SVG icons for you to use on your digital products
Data
Google search console (https://search.google.com/search-console)
Archived websites - wayback machine (https://web.archive.org/web/{timestamp}/{website}) – need to keep a copy of a site or code to illustrate your example. Replace the {timestamp} in the format of yyyyMMddHHmmss. By way of example of this format 20181028120822. Add the website you want to refer to replacing the {website} variable.
Google page speed (https://developers.google.com/speed/pagespeed/insights/)