Microsoft Windows Mobile
What it is: Microsoft's mobile edition of Windows, of course. Version 6.1 ships on phones from manufacturers such as HTC (with its Touch Diamond2 and Touch Pro2), Motorola, Palm, and Samsung.
How it works: Windows Mobile mimics full-strength Windows, complete with a Start menu and system tray. This isn't a virtue--who wants to squint at tiny icons on devices meant for on-the-go use? Manufacturers such as HTC and Samsung supplement Windows Mobile with their own software layer or with tweaks to the underlying Windows Mobile OS. For instance, several HTC devices cover up part of Microsoft's stylus-oriented interface with a fingertip-driven system called TouchFLO; it's nowhere near as elegant and intuitive as the iPhone interface, however.
How it looks: It's workmanlike. But it falls far, far short of iPhone OS's surface gloss.
Built-in applications: The version of Internet Explorer on current phones is so profoundly archaic that HTC provides Opera Mobile on some of its models. On the other hand, the productivity apps--basic versions of Word, Excel, Outlook, and PowerPoint--aren't bad.
Third-party stuff: The best thing about this OS is the sheer variety of available applications in every category. Utilities such as Lakeridge Software's WisBar Advance let you tweak the interface's look, feel, and functionality, thereby compensating for some of its deficiencies. But Windows 6.1 still has no built-in application store.
Bottom line: Windows Mobile has fallen way behind the times on multiple fronts. Windows Mobile 6.5--which delivers a more modern, touch-driven interface, a better browser, and a download store--isn't expected to show up on phones until September, and in any case doesn't close the slickness gap between Windows Mobile and iPhone OS, Android, and WebOS.
Nokia Symbian S60 5th Edition
What it is: The newest version of the venerable Symbian mobile OS, with more entertainment features and a new interface that permits iPhone-like touch input, as seen on phones such as Nokia's 5800 XpressMusic (here's a look at that phone by PC World's Daniel Ionescu.)
How it works: Like an aging platform that's been updated to reflect the iPhone era. For instance, as Daniel notes in his review, the 5800 XpressMusic retains old-fashioned scrollbars that are easy enough to manipulate with a stylus, but tough to control via fingertip.
How it looks: Decent enough, but icons, typography, and other interface details lack the refinement of the ones in Android, iPhone OS, and WebOS. It's serviceable, not beautiful.
Built-in applications: Time was when Symbian had some of the most sophisticated software to be found on any mobile device, and it's still impressive in some ways--such as the support for multitasking and cut-and-paste. But Symbian needs more updating: For instance, its browser pales in comparison to iPhone OS's Safari and other newer entrants, and its e-mail handles plain text only.
Third-party stuff: The Symbian OS has been around for so long that it's supported by a wealth of useful software, but for the most part these applications haven't been updated to make use of 5th Edition's touch-centric approach. Nokia's Ovi Store on-device software store, which launched last month, is not yet available in the United States, and reviews have been lackluster. Symbian software remains available from other app purveyors, such as Handango.
Bottom line: 5th Edition gets Symbian part of the way to where it needs to be to compete successfully with the young whippersnappers among mobile operating systems. But it needs more than a fresh coat of paint to stay relevant in 2009 and beyond.
Palm WebOS
What it is: The all-new Palm operating system that debuts on the much ballyhooed Palm Pre. Palm says that WebOS will appear on other phones in the future; rumor has it that AT&T will get a low-cost WebOS device called the Palm Eos this fall.
How it works: Overall, really well--it's responsive and fun. In some respects, it feels like the iPhone OS, such as in the way it uses multitouch input to let you resize Web pages and photos. But it also introduces features and concepts not found on the iPhone--most notably the ability to multitask multiple applications and manage them using "cards" that appear on your desktop.
How it looks: Lovely--this is the first mobile OS to compete with iPhone OS for sheer aesthetic splendor, and it appears crisp and elegant on the Pre's relatively small screen. Ultimately, I'd give iPhone OS the edge because it's less cluttered and more consistent. But WebOS is a close second.
Built-in applications: WebOS's standard productivity apps for e-mail, calendar, task manager, and the like are straightforward and useful. The most striking thing about them is WebOS's Synergy feature, which melds information from disparate sources--for instance, it can merge your Gmail and Facebook contacts into a unified address book, and enables the e-mail application to indicate whether a contact is online at the moment for a chat via instant messaging. On the other hand, the Universal Search feature--which actually searches only the names of your contacts and applications, plus Web services such as Google, Wikipedia, and Twitter--doesn't live up to its lofty name. (I was expecting it to search my e-mail, calendar, and documents, too.) Though WebOS is much less media-centric than iPhone OS, its music app is surprisingly good: You can buy MP3s from Amazon and sync directly with iTunes. But WebOS provides no mechanism for buying or renting commercial movies or TV shows for its video player.