KEYBOARD SHORTCUTS

COMMON

Works for text controls (in OS, applications, message boxes, ...), for files in explorer windows, for controls or cells, etc
CTRL+A : select all text (inside the document, the HTML control, the spreadsheet cell, etc) or select all files (explorer window, "Open/Save as" dialog, etc)
CTRL+X : cut
CTRL+C : copy
CTRL+V : paste
CTRL+Z : undo
CTRL+Y : redo
CTRL+S : save
CTRL+F : find

The following shortcuts are here for reference, though being also used in common scenarios. But they may be specific to a context and/or application, so use carefully !
These ones are known to have different behaviour than indicated here:
CTRL+N : new window/file/tab (in an app)
CTRL+T : new file/tab (in an app)
CTRL+H : find & replace
CTRL+<MouseWheel> : zoom IN/OUT, change the size of icons
CTRL+0 : reset zoom


Windows

As a reference, almost if not all Windows shortcuts available are on MS website here or here.
I just listed the ones that are or can be of use to me.


2.1. Desktop

CTRL+SHIFT+Esc : open the task manager
ALT+Tab : cycle through windows
WIN+R : run a command
WIN+L : lock workstation
WIN+D : toggle desktop/all windows
SHIFT+F10 : equivalent to the "Application" key (next to the Windows Key on the right). It's also like right-clicking an element.
WIN+KeyUp : maximize a window
WIN+KeyDown : depending on the context. If it's maximized, restore a window to its original size, if not, minimize it (in the taskbar)
SHIFT+WIN+Left/Right : move the window to the monitor on the left or right. Of course, this works only on multi monitor setups.


2.2. Explorer window (where files are listed)

SHIFT+<MouseRightClick> (on the background of a window): add menu "Open command window here" to the context menu.
Another way: type cmd in the address bar. A prompt at current location will open.

SHIFT+<MouseRightClick> on an executable file (exe,bat,...): display "Run as different user" on the context menu.

Following shortcuts list adapted from there.
Alt+Up : move "Up" in the directory tree.
Alt+D : focus the address bar and select the current path. So Alt+D then Ctrl+C to copy current path.
Alt+Left : go back
Alt+Right : go forward
Alt+Enter : properties of the selected file
Ctrl+Mousewheel : change the size of the files icons
F4 : pop up the dropdown in the address bar, showing some history, actually somewhat useful.
F11 : put explorer into Fullscreen mode. Actually kinda weird, and I have no idea why this function is even there.


2.3. calc

Toggle between modes:
Alt+2 : Scientifc mode
Alt+3 : Programmer mode
(Alt+1 and Alt+4 for resp. Standard and Statistics mode)


2.4. zit shortcuts

ALT+<MouseLeftClick>+<MouseMove> (on a window that's not maximized): drag window.
ALT+<MouseRightClick>+<MouseMove> (on a window that's not maximized): resize window.

WIN+<MouseLeftClick> (on a window): maximize window.
WIN+<MouseRightClick> (on a window): minimize window.
WIN+<MouseMiddleClick> (on a window): close window.

<MouseWheelUp or MouseWheelDown> (on the Windows Taskbar): turn the master volume UP/DOWN.


SciTE

CTRL+N : new file
CTRL+B : use abbreviations (Alt+O ; B to edit the abbreviations file).
CTRL+D : duplicate current line.
CTRL+Q : de-comment current line.
CTRL+T : swap previous line with current.
CTRL+U : decapitalize current selected text.
CTRL+SHIFT+U : capitalize current selected text.
CTRL+G : goto current line.
CTRL+F : find
CTRL+H : replace
CTRL+SHIFT+8 : toggle whitespaces display.
CTRL+SHIFT+9 : toggle line endings display. Type Alt+O ; L ; L to use LF as line ending (Alt+O;L;+ or Alt+O;L;{Enter} for CRLF) and Alt+O;C to convert current file line endings to the one picked.
  To change current line endings to LF, type Alt+O ; L ; L ; Alt+O ; C.

FireFox

<MouseMiddleClick> (on a link) : open link in a new tab
CTRL+N : new window
CTRL+T : new tab
F5 : reload
CTRL+F5 : force reload
CTRL+<MouseWheel> : zoom IN/OUT
CTRL+0 : reset zoom


Add-on specific

CTRL+ALT+T : duplicate current tab (needs TabMixplus)


Linux

#GUI #CLI <MouseRightClick> paste
#GUI ALT+<MouseLeftClick>+<MouseMove> (on a window that's not maximized): drag window.
#GUI ALT+<MouseRightClick>+<MouseMove> (on a window that's not maximized): resize window.