If you spend a long time in the Internet, chances are, you might find something useful, or, at the very least, something cool. I usually bookmark my findings in the browser, but I figured if they helped me, maybe they could help someone else.
Some are super basic, some are less known. It matters not (at least not to me). All were useful to me at some point, and I'm sharing my humble findings here. May they help you as they have helped me!