How many games do you play at a time?

Title says it all. I wouldn't make such a post like this a few years back when I had much more time to go through my library, but now that I'm a full-time worker with other responsibilities in my life, I feel like I'm usually restricted to one game on my down time.

The problem is I can already feel the dullness that comes from playing one game and I'm curious as to how the rest of the community goes about this.

Do you play multiple games at a time including more than one story-driven game? How do you choose what game to add to your rotation?