What are your favorite online resources?

Hello everyone!

We are looking to compile a list of the best online resources for Electrical Engineering to put in the sidebar/wiki. If you know of a website, guide, video, program etc. that you feel is worthy, post it below along with a short description. Resources can range from the basics all the way to in-depth analysis.

If someone submits a resource you don't agree with leave a comment explaining why, don't just downvote.

Thanks for everyone’s help making this a great subreddit! -Mod team