The K Desktop Environment (KDE) Project has released the first beta of KDE 4.1, which is targeted to fully replace KDE 3, when it goes final in July. Like other desktop open source projects focused on Linux and open source users, including GNOME, KDE presents a graphical desktop interface designed for usability. The new version has many improvements to the desktop shell and is much more configurable than version 3, as described in the release notes. The KDE Personal Information Management suite is also now ported to the new version, along with quite a few other applications. Here's a look under the hood.
Just as Microsoft Windows Vista's Aero interface organizes graphical views of key parts of the Windows desktop, KDE uses an interface called Plasma to create panels, menus and desktop components. Plasma is now much more mature in the 4.1 beta version, with support for multiple, resizeable panels and more. In fact, the KDE interface is starting to look and behave downright Mac-like, as seen here:

Kontact is KDE's personal information manager, supplying calendar and contacts functionality similar to what Windows and Mac users are used to. There is a useful new note-taking feature called KJot, a time-tracking module, and Kontact handles multiple calendars better than it did previously. KDE 3's calendaring and contact management were pretty bare-bones, but the new PIM features are competitive with what you find in commercial operating systems.
Many KDE 3 users will want to upgrade simply for the applications that come with the desktop environment. These include DragonPlayer (a very snappy media player), a new printing application, new picture browsing features, and many additions to Dolphin, KDE's file manager. Dragon Player is seen at left.
All in all, this beta is worth downloading and tinkering with. There are lots of screenshots, if you want to take a tour. You can expect the final version to arrive on July 29th.