Cut
 Copy
 Paste
 History/Notes
Apple
 ⌘ Command+X
 ⌘ Command+C
 ⌘ Command+V
Windows/GNOME/KDE
 Control+X / ⇧ Shift+Delete
 Control+C / Control+Insert
 Control+V / ⇧ Shift+Insert
 In Windows 10 if enabled: ⊞ Win+V [6]
GNOME/KDE terminal emulators
Control+⇧ Shift+C / Control+Insert
 Control+⇧ Shift+V / Control+⇧ Shift+Insert
(⇧ Shift+Insert or middle mouse button for pasting selected text)
BeOS
 Alt+X
 Alt+C
 Alt+V
Common User Access
 ⇧ Shift+Delete
 Control+Insert
 ⇧ Shift+Insert
Emacs
 Control+w (Cut / Wipe out)
 meta+w (Copy)
 Control+y (Paste / Yank)
 A "kill ring" is maintained. Multiple M-yanks rotate the ring in place.
vi
 d (delete)/dd (delete line)
 y (yank)
 p (put)
X Window System
click-and-drag to highlight
 middle mouse button