OSX.md

Go 'up' a folder in Finder

Command + Up

Peek at desktop

Fn + F11

Editing or entering a path in Finder

Command + Shift + G

Displaying hidden files in Finder

 Command + Shift + .

Locking the screen

Control + Shift + Power

on newer versions it's:

Control + Command + Q 

Switching workspaces / desktops

Control + Left/Right

Scaling text

System preferences > Display

Spotlight / Search Everywhere

Command + Space

From the command line:

mdfind    

Navigating the Menu Bar (equivalent to ALT in Windows)

Control + Fn + F2

Smaller increments/decrements of the volume:

Alt + Shift + F12