The tools you find inside are of a more generic nature. Meaning that they are not focused for one game or engine in particular. Even though they may seem to favor one over another, they really can apply to almost any project you choose. A nice place to find some gems.
Again the same thing here, the tutorials are not necessarily meant for Quake engines or Unreal. you can apply what is being said in these tutorials to many different projects. Sometimes these are the most educational. Broken up into different sections because the page would just be too big if we didn't. You can find some of the same links in different sections.