Gecko

Gecko is a layout engine currently developed by Mozilla Corporation, known as the layout engine of the Firefox web browser, Mozilla Application Suite, Nvu, Mozilla Thunderbird and many more. It is designed to support open Internet standards, and is used by applications such as Mozilla Firefox, Camino, Flock, SeaMonkey, K-Meleon, Netscape 9, Lunascape to display web pages and, in some cases, an application's user interface itself (by rendering XUL). Gecko offers a rich programming API that makes it suitable for a wide variety of roles in Internet-enabled applications, such as web browsers, content presentation, and client/server. Development originated with Netscape Communications Corporation, but soon moved to the Mozilla Foundation for the Mozilla application suite, and now used in many applications developed by Mozilla Foundation and or the Mozilla Corporation, as well as many other open source software projects. It was also used in later Netscape Navigator releases.

Gecko is written in C++ and is cross-platform, and runs on various operating systems including BSDs, Linux, Mac OS X, Solaris, OS/2, AIX, OpenVMS, and Microsoft Windows. Its development is now overseen by the Mozilla Foundation. Licensed by a tri-license of the Mozilla Public License (MPL), GNU General Public License (GPL) and GNU Lesser General Public License (LGPL), Gecko is free and open source software.

Gecko is the second most-popular layout engine on the World Wide Web, after Trident (used by Internet Explorer for Windows since version 4), and followed by WebKit (used by Safari & Google Chrome) and Presto (used by Opera)

Original article: http://en.wikipedia.org/wiki/Gecko_(layout_engine)