Unix ToolBox is a well made documentation of Unix/Linux/BSD commands and tasks for those who do not fear the command-line and want to get some extra tips. Each task or command is followed by an explanation that makes it easy for comprehension, unlike many other documents of this type.
The document is divided into several categories to ease up research – the navigation sidebar makes it easy for you to pick-out exactly what you want.
It is an ad-free, practical guide for both experts and none. I find it very helpful, and hope it can be the same for you.