There are many hints here explaining X11, X Windows, and XFree86, so I won't repeat too many details ... but basically, X11 for OS X opens up the world of GUI Unix software to OS X. Apple's implementation includes full Quartz compatability, and a nice Aqua wrapper around each window, allowing it to be minimized or docked, for example. The windows are also fully accelerated.
I downloaded and tested it yesterday with AbiWord, and it worked amazingly well. It truly is a seamless X11 environment (although you can still choose to use your own window manager if you prefer).
As an off-topic aside, thanks for those of you who stopped by yesterday at the show to say hello. It was nice putting some faces to the names. Hopefully my talk wasn't too boring!
I've got a few minutes this morning, and I'll try to post a few of the hints on Safari, but most of them will have to wait for either tonight or tomorrow morning...

