We have been busy adding support for multiple windows in TNGViewer; the current build looks quite stable, but we could definitely use some actual user testing before releasing it into the wild...
Basically, the File menu now contains a 'New' option, which will create a new, independent TNGViewer window, with its own state. This should let you view multiple models and scenes at the same time, but relatively solid iron is of course required -- if you have a modern machine and would like to test the latest TNGViewer release, please write us
specifying your platform (Win/Mac) and system (Vista/Leopard/etc.).
The usual disclaimers apply, as this is pre-release software; furthermore, if you test the build you are supposed to send us a testing report.
(A screenshot of the test build is available here