While Palm's web OS (now owned by HP) does not get nearly as much mind share as iOS or Android smartphone operating systems do, it is a contender for one of the easiest, cleanest user interfaces on the market.
Additionally, since applications can be written using Java, there is a healthy ecosystem of applications for Web OS. Web OS has many exciting features that new smartphone users may find attractive, including a spectacular user interface, syncronization, and a WebKit Web Browser.
Users who like simple user interfaces but do not, for whatever reason, like the iPhone user interface may find web OS to be an ideal smart phone user interface. With the same clean aesthetic focus as iOS has, web OS prioritizes simplicity and ease of use.
For example, the multitasking interface is in the form of "cards" that the user can slide back and forth to multitask. For example, if you have in the calendar app open and you want to switch to the contacts app, you can do so simply by sliding cards on the screen back and forth . These cards show the apps on them.
It is worth noting that even Apple journalists such as John Gruber of Daring Fireball have noted that the multitasking interface in web OS is cleaner than in iOS. While Apple may at some point introduce a similar multitasking interface, for now, web OS has a much cleaner multitasking user interface.
Web OS synchronizes your applications in the cloud. That means that, when you update your calendar app on your phone, it syncs to a server which then syncs back to Microsoft Outlook, Google calendar, or whichever calendar app you prefer. This is especially useful for business people who are on the go and often need to update their phones and keep their computers in sync with the data on the phones.
Keep in mind, though, that synchronization only works if the applications you use use the APIs that allow syncing. It is not enabled, by default, in web OS applications. In other words, apps need to provide their own servers in order to allow syncing between devices.
The web browsing experience is an incredibly important aspect of a smart phone. Web OS has this covered with a WebKit browser. The WebKit engine, which is the same engine that Apple's Safari runs, is the most advanced mobile browser engine available. It renders webpages almost exactly as they would appear on laptops or desktop.
The HP Veer
The newest smartphone that runs the web OS operating system is the HP Veer. The Veer, which is tiny (almost like the Tamogotchis of the '90s, although not *that* small) is intended to be a compact smartphone. While some reviews report that it is too small for comfort, the operating system is what is most important. Users who are in love with their hardware keyboards are in luck, as well—the Veer has a slide-out hardware keyboard.
web OS is an excellent choice for users who want an iPhone or Android alternative that is easier to use than a BlackBerry or a Symbian smartphone.