PC	MAC	Action	Browser responsible
ctrl + A	⌘ + A	Select all
ctrl + B	⌘ + B	Bold
ctrl + C	⌘ + C	Copy
ctrl + I	⌘ + I	Italic
ctrl + U	⌘ + U	Underline
ctrl + V	⌘ + V	Paste
ctrl + X	⌘ + X	Cut
ctrl + Y	⌘ + Y	Redo
ctrl + Z	⌘ + Z	Undo
ctrl + SHIFT + Z	⌘ + SHIFT + Z	Redo

Editor specific notes:
TinyMCE adds:
CTRL + 1..6: H1 - H6 respectively
CTRL + P: Paragraph

CKeditor adds:
CTRL + L: Opens the link window.
CTRL + ALT + ENTER: fits the editor to the window.

Aloha editor add:
CTRL + .: Superscript
CTRL + ,: Subscript
CTRL + \: Clear formatting
CTRL + K: Insert link
CTRL + P: Pre
CTRL + 0: Paragraph
CTRL + 1..6: H1 - H6 respectively

Google Drive shortcuts are as noted here: https://support.google.com/drive/answer/179738