Hotmail.com What's The Difference Between Yahoo.com, Ymail.com, And Hotmail.com?

What's the difference between yahoo.com, ymail.com, and hotmail.com? - hotmail.com

It yahoo.com at the end of my e-mail, but my friend has ymail.com until the end of his speech, and another hotmail.com. I know it was a decision by Yahoo, ymail, hotmail, or if we signed, but what's the difference?

All are powered by Yahoo! Right?