There are choices of free Gerber file viewers out Internet. I’ve tried some so I’ll take notes for archival purpose.
I decided to use GC Prevue btw.
Provided by GraphiCode free of charge. Working fine on my Windows 7 machine. Advertisement appears on startup but not too bad. There seems no functional limitation.
Online Gerber Viewer
This is an amazing tool. The feature is provided online so only you need is a web browser. You don’t have to install software. It works great. But I didn’t go for this tool since I’m not comfortable with network dependency. Naturally, you need to upload your file to view.
Provided by PentaLogix. Free version is available. The free version is good enough for me. I feel that graphic is less clear than GC Prevue. I was using this software for Gerber preview before.
This is a utility of an open source EDA software distributed under license of GPL, gEDA:
Nice screenshot, but I could not install it for lack of Windows support.
Provided by McCad. Free version is available but limitation is quite strict. Not for me.