There's no tool more powerful to me than great online documentation. Moreso than online question forums like stack overflow, which is a close second for me. If I can't find good docs for something, I don't use it, because I'm searching the docs on the tools I use at least three times a day. I remember a quote from Richard Feynmann taking a Anatomy class:
We're a place where coders share, stay up-to-date and grow their careers.
We strive for transparency and don't collect excess data.