What are your favorite (free) tools?

Hey everybody,

I would like to know what are your favorite free or super low fee tools you are using additionally to the website builder?

This can be tools for design-ideas, graphics, fonts or even a dead link checker. Anything you can think of. I am considering to compile a sort of megathread / list with some nice additional tools that will help us all to thrive doing websites and generate great content on them.

When you recommend a tool, let us know why you use it and what it can do. :smiling_face_with_hearts: