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
cheat.sh - The only cheat sheet you need Unified access to the best community driven documentation
Ritual Essential for Men - The scientifically-developed multivitamin for men
explainshell - Match command-line arguments to their help.
Project Gutenberg - Project Gutenberg offers free ebooks to download.