I thought this would be an interesting topic for CircuitStudio users and a great resource for those new to PCB design.
Gerber files are an industry standard, and have been for decades, for transferring design data from CAD system to PCB manufacturer. It is always good to view your Gerber files prior to manufacture - one way to spot those silly mistakes that can be hidden behind all the clutter that comes with the PCB editor of your CAD system. Contribute to this post by letting us know your favourite viewer (no paid products please - we can't advertise here!). I'll kick off with a couple, just examples of what is out there and not intended as product endorsements in any way.
An open source GPLv2 licensed project https://sourceforge.net/projects/gerbv/. A desktop application that I would classify as a traditional style viewer. Multiple layers can be loaded along with Excellon drill files and layer colours and ordering easily modified.
A very interesting program that takes viewing into the 3D realm. It's quite impressive to see your board with the layers expended out and at any angle. How useful is this? - let us know in the comment section. In addition to spreading out the layers you can select to peel back layers to reveal what's below.
The video demonstration well worth watching: https://zofzpcb.r.worldssl.net/video/Demo3a.mp4
Let's help all CircuitStudio users - enter your recommendations below. It will be interesting to see if there is a consensus or is Gerber viewing out of fashion.