UC Browser is an alternative web browser for your iPhone, specifically designed for the Chinese market.
As far as alternative iOS browsers go, UC Browser is pretty attractive. It's cuter than Safari, supports tabbed browsing, and has some neat menus. However, UC Browser is in Chinese, with no language choice available. There is a version in English available here.
The biggest issue with UC Browser is that pages are optimized by the developer's servers, in a similar way to Opera Mini/Mobile. However, many pages do not render very well when compared to Safari, and many sites seem not to recognize UC Browser as a mobile app, so you end up with a mangled version of the desktop website you were looking for. Another issue is that UC Browser suffers from censorship, meaning some sites are simply not available in it (Gmail is prominent example).
If you're looking for an alternative to Safari on iOS, Opera Mini or Skyfire are much better and more user friendly options if you live outside China.
UC Browser is an app that is really only suitable for usage within China, as its web page rendering and limitations mean it compares badly to Safari and others.