Call it Zynga Anxiety: A thrilled yet disquieting sense that you’ve built a billion-dollar web business that’s almost entirely dependent upon another company’s platform.

For browser toolbar provider Conduit, the audacious self-prescribed cure was to develop its own platform – its own damn browser – in an effort to hoist itself up a notch on the software stack. Today, Conduit’s U Browser went into a public, unplanned and rather premature beta. Try it if you’re on a Windows PC.

When I met with Conduit CEO Ronen Shilo in the spring to discuss his roadmap, Shilo was perfectly candid about the fact that the toolbar business, while insanely profitable for the company, does not represent Conduit’s future. The next stage for Conduit has to include two elements: an end user-centered product that adds genuine ongoing value (unlike toolbars, which are publisher and Conduit-centered), and independence from inherent IE, Firefox and Chrome restrictions.

U Browser is Conduit’s most ambitious effort to date to break out of the toolbar model and achieve this goal. A few months ago, Shilo was already quite stoked about it, but asked me to hold off on reporting the browser until it was more fully baked – more than it still is. U Browser’s big product launch was not supposed to go down like this.

At an internal company meeting yesterday, the U Browser product team presented an open version to peers, and when a few tried out its Facebook sharing, eagle-eyed Israeli hackers and Hebrew tech media pulled the cat out of the bag. So non-official launch day it is, though the current beta product lacks some essential planned features (including Mac support).

At this stage, U Browser most closely resembles Andreessen Horowitz-backed RockMelt – it’s based on Chromium (so all Chrome addons should work) and integrates a social layer directly alongside the browsing experience. U Browser has a nifty right-panel element that lets you switch easily among your Facebook news feed, Facebook chat, Twitter feed and YouTube channels:

That element is where U Browser soon hopes to shine, as it encourages developers to build apps and integrate their services directly into its browser.

Conduit has been working with a bunch of top consumer web services to build custom apps for U Browser, which aspires to become a type of web-centered desktop, like Google’s Chome OS. But while in Chrome OS the operating system reaches out to incorporate the web, U Browser goes in the other direction – the browser swallows up the desktop, and can do so on any OS.

Aside from those desktop and web service integrations, we’re still not seeing two other planned aspects of U Browser that could be game-changers: (1) for mobile, smoother integration of web services to the browser, and (2) a ‘lean-back’ mode for web browsing and app use on your TV, from the living room couch.

The latter feature could end up being the key differentiator in a browser market dominated by the giants, especially if widespread PC-TV convergence occurs at a rapid rate that catches Google, Microsoft, Apple and Firefox without a thoroughly rethought browser UI. That’s where U Browser’s greatest potential lies – with a healthy budget and very talented team behind it, Conduit’s product can radically reassess what the browser experience should be for today’s devices, apps and users.