Windows 10 comes with a built-in app, Mixed Reality Viewer, which allows viewing different 3D models. It comes bundled with modern versions of the OS. Insiders on the Fast Ring are getting an updated version of the app, which is renamed now to 3D Viewer.
Starting in Windows 10 Build 17115, Windows 10 features a number of improvements made to the built-in Windows Mixed Reality feature. All these improvements will be included in Windows 10 version 1803, which is coming to the stable branch this March.
Starting with Windows 10 Creators Update, there is a new feature - the Windows Holographic platform, which has a special icon in Settings. There is also a built-in app, Windows Mixed Reality Portal. If it can't find the required hardware, it doesn't start. Here is a tweak which will allow you to disable the Mixed Reality Portal hardware checks and run the app.