Nate Trost correctly mentioned what I would consider to be the shocking secret of the Apple II Video Overlay Card: when placed in an Apple IIe, it allows you to have access to, and fully use, all the graphics modes on the Apple IIgs! I wonder if any software was ever written to take advantage of this. Somehow I doubt it.
It's essentially a packaging of the graphics chip found in the IIgs onto an expansion card. When placed in the IIgs, it worked in tandem with the built-in graphics chip to give you interlaced support (doubling the vertical resolution for super hi-res graphics). I believe it also allowed you to overlay actual video (e.g. from a video camera or other input) onto the IIgs screen. I could be wrong on that last point though - I haven't cracked open my card to see; I've been too busy lately.
I did finally turn on my Apple ///+ this past weekend. It mostly works, but 80-column mode is very broken. It stays fixed in 40-column mode no matter what. I've ordered some replacement chips for cheap; hopefully this will do the trick. This is a hard machine to troubleshoot as you can't easily run it with the motherboard fully exposed. I hope to post some pictures as time permits. It's pretty hard to get much more than a token press release blurb of info on the Apple ///+ off the net, and pictures are rarer still.
Speaking of hard to find, Apple designed a color RGB monitor to work with the Apple ///, which has a unique RGB port. This monitor appears to be unbelievably difficult to find. I believe it was called the Applecolor Monitor 100. It basically looked like a really fat and bloated Monitor II and had a motorized tilt screen. I cannot find any pictures at all of this on the net. I believe the Apple model number is A9M0308. If you have one of these, I'd like to talk to you. :-)
