GrabCAD offers a way for engineers to collaborate by providing easy storage and access to a huge library of 3D computer aided design files. I have written on their blog, and occasionally poke around their library for models of various uses. One feature it is good to see them focusing on is the mobile app. Viewing on a mobile app is important for companies that are looking to the future. Editing from a mobile device is still limited, they lack the software and processing power to run most existing programs, but maybe GrabCAD will be the ones to change that. Until then you can use their app for handy viewing of all their files (or your own, if you are logged in and sharing).
I was able to easily download the GrabCAD app from the Apple app store. Once opened you can immediatly browse the library of 3D files in the libraries, each uploaded by various other users. All public files are also downloadable to a embedded viewer that allows for simple zooming and turning of the model. The viewer can not hide parts, do section views, or edit the file but for a simple display it does the job nicely.
Signing in provides individual access to private files or those shared on a corporate account or with limited groups of others. The app does occasionally crash and could use additional features for commenting, marking up, and editing the models but overall it serves the need of having an easy and free way to share 3D files with a large group of people.