Global

cmd + tab - switch between apps

cmd + tab, then option - show minimised app

cmd + shift + / - open the help menu for app

Finder

cmd + shift + . - show/hide hidden files

DNS

Check active DNS

scutil --dns

Flush DNS cache

sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder

Configuration

Set computer name

sudo scutil --set ComputerName "newname"
sudo scutil --set LocalHostName "newname"
sudo scutil --set HostName "newname.local"