Microsoft Maquette is a general purpose mock-up tool for spatial prototyping within virtual reality. It was built from the ground up to empower anyone to create fully immersive concept sketches in VR from inside your headset. Maquette includes a set of tools for importing, creating, composing, and storyboarding content in 3D space, complete with a library of primitives and UI icons. Among many other features, Maquette has fast and approachable UX, a text tool for annotations and spatial UI mockups, and easy selection and nested-grouping of content. Maquette has a complimentary Unity addon for importing Maquette content into Unity, which preserves materials and grouping hierarchy. Maquette's development process is guided by users' needs, so we want your feedback!

Maquette's Website
http://www.maquette.ms

Bringing Maquette Content into Unity
https://www.maquette.ms/unity-addon