What's the name of the html doc style which has 2 columns?

[ahmedeqbal]

Here are 2 sites using this 2 columns style which I can't tell a name:http://documentcloud.github.com/underscore/docs/underscore.htmlhttp://momentjs.com/docs/They're beautiful and I want to know the name of this kind of style and is there any template/tool to create this kind of document? Thanks.