[inconditus]

Interestingly enough, Chrome had this option in the developers page, but they removed it. I believe it was called horizontal side tabs.

[WesleyJohnson]

I have this option with Chrome 13.0.782.109 beta-m. If you right click a tab, the context menu option is "Use Side Tabs". I just can't remember what I did to get that option to appear in the context menu. I thought I used "about:labs", but that is no longer showing anything. Maybe the feature is baked into this build?

[elxx]

It's the first item in "about:flags".