Invision - Prototyping and collaboration for design teams
CGTrader - CGTrader is an online marketplace at which artists can sell and buy Revit and 3D models.
Mockuuups Studio - Fast and easy way to create product mockups on macOS, Windows and Linux.
3DExport - 3DExport is a 3D model marketplace where you can buy and sell 3D models, CG textures and digital objects for 3D printing with royalty free. Professional 3D models - 3DExport.com
Craftwork - A collection of User Interface resources made by Craftwork
TurboSquid - TurboSquid offers 3D models for professionals.