Arora is a lightweight cross-platform web browser. It's free (as in free speech and free beer). Arora runs on Linux, embedded Linux, FreeBSD, Mac OS X, Windows, Haiku, and any other platforms supported by the Qt toolkit.
Apart from the must-have features such as bookmarks, history and tabbed browsing Arora boasts:
very fast startup
integration with desktop environments
smart location bar
flexible search engine management
WebInspector, a set of tools for web developers
Arora began as a demo by Benjamin Meyer to help test the QtWebKit component, but since then it has grown into its own project outside of Qt.
Arora has a small, simple code base that is fun to hack on. Join the party in #arora on irc.freenode.org!