This is a great application.
At first, I was impatient and thought it was not usable at all.
But I gave it a chance.
This is a quick-start guide for PCB-nerds:
I had gerber files made from OsmondPCB, and I wanted to view them. As you probably know, there are very few options on a PowerPC based Mac.
When I first opened Cenon and tried opening the Gerber files, I saw they were all gray. I tried to 'force' Cenon to open the files, by setting "Always Open With" from Finder. No dice.
-Then I looked at the /Library/Cenon/Examples/Gerber/cpu.ger
"Oh, it has a .ger" extension. I renamed my Gerber files, and Cenon would read them.
Alright.. How about importing multiple files then?
-Yep, all imports on top of eachother. I quickly found out that you can in fact have separate layers (see the inspector panel) - this is excellent.
Now, I used a wrong approach on the colorizing. I wanted each layer to have its own color, so the silk screen would be yellow, the copper layer copperish and the mask green. I quickly found out that I could not just select all, and then colorize. So what I did the first time, was to select by hand, all those parts that are of the same kind (eg. all rectangles) then colorize them, then select all the circles, colorize them, etc..
Later I found out that I only need to select a single object, then press Command-E to select all that are of the same kind. I could then quickly colorize the entire layer.
Finally: I also found out that since the gerber output layer sizes differ, due to that they do not have an outline specified; I could place a square in each corner, which would make each layer larger. I would copy all 4 squares to each layer on the PCB, and then export the Gerber files from Osmond. Now they import as the same size in Cenon, and everything looks quite good.
Board outline can ofcourse be drawn in Cenon using a plain rectangle and then change its width / height in the inspector panel.
Cenon is definitely worth trying out (and if you don't know OsmondPCB, you should check it out; TIMESAVER: Remember to read the documentation first; double-click the toolbar buttons!!).