A Few of our Favorite Modes

It's show-and-tell time for our favorite Emacs modes. We'll share tips on the features we rely on most! I've got mine: Helm, Projectile, Magit... What are yours? Here's some ideas:

• The Awesome Emacs list: https://github.com/emacs-tw/awesome-emacs
• Quora thread on "Most Useful Extensions": https://www.quora.com/What-are-some-of-the-most-useful-extensions-for-Emacs

Post yours below (or just show up!).