Via gbXML.org newsletter from 2018-10-16:
A new version of the free web-based gbXML viewer from Ladybug Tools has been launched. This viewer allows you to upload any gbXML file and view it in any browser on any device, whether it is your laptop, smartphone, or tablet. You can also zoom, pan, rotate, hide elements, and even edit your model.
Some of the new features include:
  1. A “Reports” button that displays the total quantities of zones, spaces, surfaces, and openings in a model, in addition to basic campus and building attributes.
  2. An “Issues” button that displays lists of duplicate adjacencies and surfaces, invalid surface and opening types, and more “problems” with the model.
  3. A first-person camera view
  4. Sun-range functionality

This free and powerful viewer is available at this link.