EasyEDA’s Free and Online Gerber Viewer
EasyEDA is a cloud-based EDA tool suite which supports open source and working collaboratively. Tools from EasyEDA include circuit simulation using Spice, PCB design, electronic circuit design and now RS-274X (Gerber) and Excellon gerber viewer, all are free. To use this viewer you need to upload your gerber files, in RS-274X format, in a zip file.
EasyEDA’s gerber viewer allows zooming in/out the imported gerber files, choosing the color of PCB, exporting to image, enable/disable view of layers (files) of gerber, sharing the gerber online using the URL after uploading the files and showing some analysis data (Design for Manufacturing DFM) from gerber files like the number of layers, hole and track sizes, clearances and dimension of board.