I hope you have heard of Slack. Because everyone (at least in the tech, personal development, and business world) has. It’s evolved into a replacement for email between people who want to talk to each other in a company. The problem is that email gets really messy when the conversation starts getting long. You have to dig through tons of nested emails to find what you need. Plus, sending documents, attaching files, or communicating with a group of people makes it worse. Slack solves this by being something in between email and instant message. Messages and files sent to a group of people or a single person are neatly organized and clear as day. On top of that, there are customizations you can add to make it your own. You can have it alert your phone with the app or pull up a GIF if you're feeling funny.
For a more philosophical approach to productivity, dive into this classic self-help book that's sold millions of copies worldwide. Covey takes Allen's methodology a step further, offering a guide to better life and work habits.
This browser extension is a life saver. A lot of successful people emphasize the power of focusing on one task. This app greets you and asks you what your main focus is. Each time you open up a new tab, the app pops up and reminds you to stay on track. It replaces the browser tab that is there by default that usually tempts you to go to unproductive websites.