layout engines

• Trident 

Trident (layout engine)
Trident (also known as MSHTML) is the name of the layout engine for the Microsoft Windows version of Internet Explorer.
http://en.wikipedia.org/wiki/Trident_%28layout_engine%29

• WebKit

WebKit is layout engine software designed to allow web browsers to render web pages.
It powers the Apple Safari and Google Chrome browsers
Opera have announced that their browser will also move to use it
It is also used as the basis for the experimental browser included with the Amazon Kindle e-book reader, as well as the default browser in the Apple iOS, Android, BlackBerry 10, and Tizen mobile operating systems
http://en.wikipedia.org/wiki/WebKit

• Gecko 

Gecko (layout engine)
Gecko is a free and open source layout engine used in many applications developed by Mozilla Foundation and the Mozilla Corporation (notably the Firefox web browser), as well as in many other open source software projects
It is designed to support open Internet standards
http://en.wikipedia.org/wiki/Gecko_%28layout_engine%29