These are the two rendering engines that drive most web browsers today.

Trident (IE’s Rendering Engine):
http://en.wikipedia.org/wiki/Trident_(layout_engine)

Gecko (Firefox’s Rendering Engine):
http://en.wikipedia.org/wiki/Gecko_engine

Check out these posts too:

  1. Web Developers should be using XHTML
  2. Download the entire Wikipedia wiki.
  3. Super Elastic Bubble Plastic from the 70's and 80's
  4. Can you visualize Pi?
  5. Page Headers tool now supports user selected Agent
  6. File this under no way in hell
  7. Test websites in IE6, IE7 and IE8 with IETester