Cortana is the Windows 8.1 voice assistant which is in beta. recent releases added it to many other regions like India. Here is a video which shows 50 voice command for the Cortana
Cortana is your personal assistant on your Windows Phone. She's there to help make things easier for you and keep you up to date on the things that matter to you.
From the same publisher here are two other videos which will cover 50 Voice command for Siri, the iPhone personal assistant
Now the Google Now voice commands for your Android Phones. You may try the Google Now Launcher and say “Ok Google” to trigger the input and use it
Have you ever used a personal assitant like the Cortana, Siri or Google Now ? and what is your experience ? please share with us.