Win — opens the Start Menu, in Windows 8.1 — opens the previous window;
Win + A — opens the Action Center (in Windows 10);
Win + B — selects the first icon in the Notification Area (you can then switch between the icons using the arrow keys);
Win + Ctrl + B — switches to a program indicating a new message in the Notification Area;
Win + C shows the Charm Bar (in Windows 8 and 8.1); in Windows 10 it opens Cortana (if you’re using a supported language);
Win + D — shows the desktop (immediately minimizes all the opened windows);
Win + E — opens Windows Explorer; in Windows 10 opens the Quick Launch by default;
Win + F — opens ’Find files and folders’;
Win + Ctrl + F — opens ’Find computers’;
Win + G — brings all gadgets to the foreground that are in process (only in Windows 7 and Vista); opens the Game bar in Windows 10;
Win + K — opens a new Start menu — Connections (in Windows 8 and 8.1);
Win + L — changes user or locks the workstation;
Win + M — minimizes all windows;
Win + ? Shift + M — restores windows that were minimized;
Win + O — locks device orientation (disables the gyroscope function on tablets);
Win + P — switches operating modes to an external monitor/projector (only in Windows 7 and newer);
Win + Q — opens Search charm for installed apps (checked in Windows 8);
Win + R — opens the ’Run dialog’ box;
Win + T — switches focus to the Taskbar (only in Windows 7 and newer);
Win + U — opens the Utility Manager;
Win + W — opens Windows Ink Workspace (notes, screenshots);
Win + X — opens the Windows Mobile Application Center (only for mobile computers in Windows Vista and 7);
Win + Y — starts Yahoo! Messenger (if installed).
OS X keyboard
Command + Up Arrow — Immediately scroll to the top of any webpage.
Command + Down Arrow — Immediately scroll to the bottom of any webpage.
Command + Semicolon — Cycle through misspelled words in any given document.
Command + 1 (2, 3) — Use this shortcut to conveniently cycle through any open tabs you have in your browser. Command + 1 will take you to the first tab, Command + 2 will take you to the second, and so on.
Option + Delete — This handy keyboard shortcut will delete words one word at a time, as opposed to one letter at a time. This works all across OS X, whether you’re typing in TextEdit or even when typing a website into your browser’s URL bar.
Command + H — Quickly hide all open windows from the currently active app.
Command + Shift + T — Instantly open up the most recently closed tab in your browser. This is a lifesaver if you accidentally close a window and can’t remember the URL.
Option + Shift + Volume Up/Volume down — Increase or decrease your machine’s volume in much smaller increments. This comes in especially handy when you’re trying to get your audio output levels just right.