Pull out your smartphone and scroll through your list of recently downloaded apps. What do you see — Snapchat, HQ Trivia, or maybe some random face-filtering nonsense? Is Signal in there? If not, you've messed up in a major way. Despite all the cool games, video editing tools, and shopping-assistant applications released this year, the secure messaging app Signal is the only one that really mattered over the course of 2017. And it wasn't even released this year.