Does anyone know what Apple Mail is written in?
I'm trying to determine what component it uses to render HTML, is it using the Webview Class?
Are there any other options to render HTML when building OS X applications?
It's an Objective-C/Cocoa app and it's using WebView.
I know secondhand (from a developer who was tracking down bugs in his app and comparing behavior to Mail) it takes advantage of some undocumented calls to accomplish certain things. But for the most part it's the same WebView that you've got access to.
If you'd rather render HTML a different way, you could check out Gecko, the engine/library that Firefox and Camino are based on.