.sxw. Clicking on it baffled OS X, so I asked around and someone pointed me at NeoOffice/J, which is part of NeoOffice. I got a hurried and entirely opaque explanation of how this is using Java/Cocoa magic to sweep the Open Office X11 under the carpet, but hey, it seems to work, despite lots of “This is a Beta!” warnings. It handled the .sxw, and then I pointed it at a .doc and a .xls and it was fine with those, too. The only downside so far is it doesn’t have the real Aqua look.