Mobile devices have been influencing desktop software design for several years now. Mostly, I've not been impressed. Either the results are awkward, like GNOME 3, or over-simplified, like Ubuntu's Unity.
I had just about reached the conclusion that the mobile influence represented a step backwards in desktop design -- then I tried KDE's Plasma Active, a desktop designed for touch screen tablets, and all my assumptions were trampled underfoot.
Quite simply, Plasma Active is not only an elegant solution for small screens, but also for screens of any size. By any standards, it's an example of effective desktop design.
Unlike other recent desktops, Plasma Active is neither a conceptual re-design nor a new beginning. Rather, it is a sub-set of KDE -- a shell underlying the technology and concepts found in other incarnations of KDE.
The sub-set is missing some features, notably the standard KDE shortcuts, but, as with the earlier Plasma Netbook, nothing should prevent Plasma Active from eventually being available as an alternate view on a standard KDE desktop.
You can install Plasma Active in a virtual machine, or using openSUSE 11.4. However, for the curious, the easiest way to explore it is through two Live images for flash drives, one based on openSUSE, and one on MeeGo. Instructions are given for transferring the images to a flash drive, running them in a virtual machine, and under openSUSE.
Of these two images, the MeeGo edition seems to have been built with one or two features missing. Both are designed to run on tablets, although you can install them on any computer.
The only catch is that, to highlight the touchscreen capabilities on the Live images, the mouse cursor is deliberately transparent. You can enable another cursor theme if you can get to System Settings -> Workspace Appearance -> Cursor Theme. But, in the absence of KRunner or a user name or login to use with a command line, this task takes patience, skill, and a steady hand as you attempt to navigate with an invisible cursor.
Plasma Active opens by displaying a short introductory video. You can probably figure out the basics of the desktop by yourself, but the video will call your attention to one or two features that might be otherwise overlooked. Even more importantly, the introductory text and the video itself will call your attention to the importance of Activities, or virtual desktops.
Activities are a feature that have been emphasized ever since the release of KDE 4.0. Essentially, Activities are separate desktops, each of which can be individually customized with its own wallpaper, widgets, and icons. Each can be designed for use with a reoccuring task, such as coding, a specific location, or a particular project -- and, unlike GNOME's virtual workspaces, KDE Activities can be saved for later use.
The idea is a sound enough, although taking full of advantage of Activities does require a rethinking of how you work. However, from the start, KDE has struggled to present Activities in a way that makes the concept attractive and easily available to users.
The first effort was to present them in an overview similar to GNOME's, but that seemed only to baffle users. The next was to display them in a horizontally scrolling window like the one used to display available widgets. That effort was more successful yet still tended to hide activities from users.
Now, in Plasma Active, KDE seems finally to have hit on the right display. Instead of an overview or a separate window, Activities display as a rotating wheel of thumbnails, each with its name prominently displayed, and the current selection four times the size of the rest.
When not in use, the Activity switcher slides back to an inconspicious tab on the right side of the desktop. Meanwhile, the current Activity displays at the top left of the screen, alongside two buttons for selecting applications and widgets to add to the current activity.
In the openSUSE version of Plasma Active (but not Meego's, for some reason), the Activity switcher's tab is complemented by a tab on the left for recommendations of what you can do on an Activity. This feature is similar to KDE's existing Device Notifier, which displays what you can do with an external device when it is plugged into a USB port, so its purpose is immediately obvious.