Mechanical engineers now have the option of placing 3D versions of their designs online and allowing others to review and post comments. Startup GrabCAD says its product -- Workbench, now in beta -- opens up a new avenue for collaboration. Until now, it has been hard to share, said GrabCAD's Rob Stevens, vice president of sales and marketing. "And if you can't share, you can't iterate. And if you can't iterate, you can't go fast," Stevens said.