Microsoft’s Trident, Mozilla’s Gecko, Apple’s WebCore/JavaScript Core. If you’re a web developer, these are the only web content (HTML/XHTML/CSS/JavaScript) rendering engines that you’re going to need to check your pages in by the end of this year. Here they are in order of importance:

(1) Microsoft’s Trident is used in Internet Explorer for Windows. It’s important because it dominates general web browsing, and because nearly all Windows applications use it to render web content. (What about the excellent Tasman, used in IE/Mac? I’d put it in fourth place, and consider it optional.)

(2) Apple’s WebCore and JavaScriptCore — the guts of Safari — are Konqueror’s KHTML and KJS, respectively. It’s important because it will dominate Macintosh web browsing, and because nearly all applications that render web content on Macintosh will be using WebCore/JavaScriptCore — to render web content. Plus, by using Safari you’ll get a very good idea of what your content will behave in KDE’s Konqueror web browser.

(3) Gecko is used in AOL’s Netscape web browser. It’s important because Gecko is the second most popular rendering engine for general web browsing (albeit far, far behind Trident), and will be the most popular browser for AOL users.

The fallout is already starting. Omni Group, a small company that makes beautiful software, has effectively (and thankfully) announced that they’ll be abandoning OmniWeb’s poor rendering engine for KHTML via Apple’s WebCore and JavaScript Core. [via Daring Fireball] Expect iCab and Opera (which almost nobody outside of our industry have even heard of) to be completely lost of the shuffle by 2004.