I have an XBox one that links to my account. I originally did it hoping that people that I know that play XBox will see my name and then add me as a friend on XBox where I have very few. It's been a complete fail in this regard.
As for ones that I actually use, well there are none. There is a juggling game that I like but rarely play now, scrabulous sucks now that they got sued, word twist is fun but all my friends are terrible. TBH, I can't think of a single app that I frequently use.
diddy