Since Kathrine seems to have stopped doing Mac builds of Cool VL Viewer, and since I finally got a newer Mac, I decided to try to build Cool VL Viewer on it. It failed right out of the box, saying there wasn't any 10.6 SDK on the machine. I asked a friend who is much more skilled for programming than I'll ever be to help. He tried, and finally gave up: my Mac has the latest Mac OS X installed (10.9, a.k.a Mavericks), and there doesn't seem to be any way to install a working 10.6 SDK on it. He apparently succeeded to get one, but it was unusable: nothing would compile against it.
So for now, it seems to be dead, unless someone with a Mac with a previous version of Mac OS can give it a try.
So I'm stuck with Singularity now. It's impressive to see how Henri got everything right when you try to use another viewer (I had forgotten how awkward it was to have to open the chat window to change your group tag, or how annoying it is to have the escape key resetting your view…).