1
F-keys as app switcher
My best Mac/PC productivity tip for the world would be: assign your most used apps to F-keys (e.g. with Apptivate), and use them instead of ⌘+tab.
I have, for example:
F1 for iTerm, F2 for Atom, F3 for Chrome, F4 for nvAlt, F5 for Slack, F6 for Skype, F7 for Airmail 3, F8 for iTunes, F9 for NewNewsWire, F10 for The Hit List, F11 for Telegram, F12 for Finder
Extra tip: if you configure Apptivate to hide the app if it's already in the foreground, you get also a nice "poke into" functionality: for example, I press F6 twice to quickly check whether there are new messages on Skype (I'm usually DnD), and immediately get back to where I was.