Although you'll occasionally come across someone who uses Opera, the world of browser users consists largely of people using Internet Explorer, Firefox and Safari. However, for niche applications, fast performance, and for other reasons, many free spirits use some of the unusual open source browsers out there. Here, you'll find four of them, and what they're good at.
1. uBrowser

uBrowser is an open source browser concept based on Mozilla's Gecko rendering enine, but, get this, it uses OpenGL to render web pages as cubes, and in other bizarre shapes. Why would anyone want to do this? For the same reason people climb Everest--because it's there. Seriously though, uBrowser isn't meant to be used as a dedicated browser. It's a test application, and gets used within other applications.
2. Shiira

Shiira is an open source Mac browser that many people favor for what it doesn't do rather than what it does. It has privacy features that allow you to not have cookies and your browsing history recorded if you choose. It's based on Webkit, written in Cocoa, and licensed under BSD.
3. Camino

Camino is a Mac open source browser based on Mozilla's Gecko rendering engine--the same one that powers Firefox. It's favored by many Mac users for its lickety-split performance. In fact, quite a few of the open source browsers attract people because they are lightweight and speedy. It also just came out in a new version.
4. K-Meleon

K-Meleon is an open source browser for Windows that is also based on Mozilla's Gecko rendering engine. It's lightweight enough to carry on a USB key, and released under the GNU General Public License.