cheat - Cheat allows you to create and view interactive cheatsheets on the command-line.
Glose for Mobile - A social reader for ebooks, now on Android
TLDR pages - The TLDR pages are a community effort to simplify the beloved man pages with practical examples.
Project Gutenberg - Project Gutenberg offers free ebooks to download.
explainshell - Match command-line arguments to their help.
Ritual Essential for Men - The scientifically-developed multivitamin for men