With an increasing number of CAD packages now being released on more than one operating system, I find myself writing multi-OS ebooks. Usually, there are not sufficient people using Linux and OS X versions of CAD packages that are dominant in the Windows world, like AutoCAD and Bricscad for me to write ebooks specific to each operating system.
My solution is to write one ebook, and then point out differences when they occur in the the different OSes. For instance, writing about customizing AutoCAD, I put OS X-specific material in gray text; when it's a larger topic, I'll give the OS X part its own text box.
This is no problem for software from CAD vendors that chose to maintain a common look'n feel among their different OS versions, such as Bricscad and Graebert. For someone like Autodesk who took the opposite route (make the CAD software look like the OS in which it is running), I publish screen grabs of UI elements, such as dialog boxes, from both Windows and OS X, and place them side by side -- with a caption pointing out the differences.
I use InDesign as my desktop publishing software, and I have legit versions for both OS X and Windows. I find OS X clunky, however, and so I write my ebooks on my triple-monitor Windows workstation whenever I can.
This leads to the problem of how to get screen grabs (and sometimes text) from the Mac mini computer to my Acer desktop computer. The ideal situation is to simply save the PNG files over the network, but I find OS X isn't reliable in wanting to make the connection. For a while I sent the files to myself by Gmail, out of frustration.
A better solution than Gmail is to use DropBox: save the PNGs to the Dropbox folder on the Mac, and then a short time later they appear in my PC's Dropbox folder. (I would be using SugarSync, but on the Mac it keeps telling me something is wrong and I need to reboot the Mac. Solution: use DropBox instead.)
This issue of transferring files is less of a problem with Linux, which connects to networked PCs more easily than Macs or even Windows. Also of note: the screen grab software that comes native with Linux is better than that written by Apple or Microsoft.