Stacks

In Desktops a folder can be either a normal folder which opens as a new window in the Finder or as a Stack which you can navigate from a popup window in Desktops (stacks can be opened in the Finder by default by a setting in the preferences).

You can change the display of any folder by contextual clicking on the folder and checking the Show as Stack item.

In the preferences you can make all folders stacks by default (this can be changed in the contextual menu later) by checking the Show all folders as stacks box.