Monday's Riddle! A fun one!

Here's the riddle this week! Good luck ~F

Up and down I take your mood.
I make you smile, or sometimes brood.
Step in time to my prose and rhyme;
Some sway, some lurch, some skip in line.
Whatever you like when you want to move,
I'll find a beat and set your groove. 

Check back later if you need to get a clue...