WebKit

• http://webkit.org/

• Web browser engine. Application framework that can be used to develop web browsers.

• License: portions in LGPL and others in BSD. Proprietary applications allowed.

• Used in Apple's Safari browser. Many applications (browsers, e-mail clients...) are already using WebKit: http://trac.webkit.org/projects/webkit/wiki/Applications%20using%20WebKit

• Multiple graphical back-ends: Qt4, GTK...

• You could use it to create your custom browser.