Non-Affiliate Links
Training and Capture The Flag:
Offensive-Security
Applied Network Defense
The Cyber Mentor
Pentester Academy
PentesterLab
Hack The Box
Try Hack Me
Over The Wire
CTF Time
Book Publishers:
No Starch Press
No Starch Press has frequent sales. Buying a physical book gives you access to an electronic format (PDF as well as others, usually) copy. These books are all pretty high quality.
Packt Publishing (Free Learning Link)
Packt Publishing doesn’t bundle e-books with physicals. Unless there is a book you really, really want in physical format, I recommend just doing the e-book. They have a subscription fee for access to their full library with a few limitations. They do a daily free e-book give away (direct link above) which is worth watching. Quality varies, but in general these are not as well written as the No Starch books.
Tilted Windmill Press
Tilted Windmill Press is Michael W. Lucas‘ publishing company for the books that aren’t published under No Starch Press. If you missed this because you live under a rock or something, Michael is one of the best tech writers on the market. He thoroughly researches his material as he writes, gets subject matter experts to review and critique early copies, and he uses just the right level of humor to keep some of the driest material engaging.
Business Improvement
Mentor: Nicole Walters
1K in 1Day (Registration is closed most of the year.)
Fierce Clarity
Mentor: Chalene Johnson
Marketing Impact Academy (Registration is closed most of the year.)
Virtual Business Academy (Registration is open all year.)