Apple's OS X 10.9 Mavericks looks nice and shiny and new, in all the ways that new operating systems usually do. But it's got one big fix for what had been the single stupidest thing in all of OS X for the past two years. That's multiple displays.
Until now, Apple's OS X full screen apps, which it introduced in Lion, were useful to drill down into a single app, eliminating distractions (sort of), but if you were using a second display, it would totally eat your second screen. Like this:
It was aggressively stupid. Now, though, you can also get at your menus and dock from any display, and operate spaces independently on each display (if you want). It seems like a great way to use two displays, and even better than how Windows 8 is operating its metro/desktop juggling act right now.