Late last night, Reddit user u/rajadain found that when he opened the newly updated Google+ app on his 2013 Nexus 7 running the Android L preview, the app opened in a not-so-full-screen window. In fact, Reddit user u/jarshark found that this also worked with the new Newsstand update (though it crashed after it got through the welcome screen).
This windowed mode continued to persist, even after restarting the tablet. According to another user, u/titleunknown, this windowed-mode also appears on a Nexus 10 running KitKat for both Google+ and Reddit Flow, however no pictures have been provided as proof as of yet.
This bug/feature has surfaced at an interesting time, considering just yesterday Android Police had an exclusive explaining a multi-window mode the Google has been working on. Unfortunately, they provided no information as to if or when this feature would see daylight. All we know now is that Google is working on it.
While this definitely does not work like the windowed mode explained in the Android Police article, it might be a step in that direction. Right now, it is just a smaller window on the screen. It can’t be snapped to one side, and another window can’t pop up alongside it. In fact, I would compare this to ParanoidAndroid’s floating mode.
For right now, this feature isn’t all that useful, but hopefully we will learn more in the coming weeks as Google further fleshes out Android L and their Nexus device(s).