- An office, with a door I can close
This was going to be a big list, but I actually think that just about sums it up. The cube environment at Google was utterly intolerable, and made it hard to concentrate. It didn't help that the guys in another group next to us had a game where they flew rc drones around for fun, or the folks on the other side of my group that were always discussing food, or the loud door to a lab behind my desk that was constantly slamming, etc, or just the constant stream of people walking by my cube.
At home I have a door that I can close. I can think. So I get a lot more done.
I'm not saying all office environments were terrible. Before 2001, I worked doing research at a University and I had a fantastic office with a door. I think I was just as productive there as I was at home. Because, again, distractions were minimal.