COffscreenHTMLRenderer is a class with a simple API that uses WebKit to produce NSImages (or WebArchive objects) from HTML (either via a NSURL or a WebArchive). As I mentioned the API is very simple:
COffscreenHTMLRenderer *theRenderer = [[[COffscreenHTMLRenderer alloc] initWithURL:[NSURL URLWithString:@"<someurl>"]] autorelease];
NSImage *theImage = [theRenderer renderedImage];
Note that sending the renderer the renderedImage message will cause the program to block until the HTML is full downloaded. This keeps the API simple but can cause a bad user experience. The renderer can also take a WebArchive object as the HTML source. This could allow you to produce thumbnails of .webarchive files. As well as taking an WebArchive object as input the renderer can also render HTML into a WebArchive. This provides an easy way to create .webarchive files (obviously converting a WebArchive into a WebArchive may not be so useful). An interesting project would be a command line tool that downloads an webpage from a URL passed in as an argument and saves the content as a .webarchive file.