Probuilder is a Unity toolset that was developed by ProCore company which is composed of 3D modeling and level design tools, optimized for building simple geometry, detailed editing, and UV unwrapping as needed. Overall, with Probuilder you get to Greybox infinite of prototype structures in short span of time which means you can model inside of Unity Engine instead of going back and forth from 3D application; develop complex terrain features, modeling vehicles/weapons/props, or make custom collision geometry, trigger zones, and nav meshes.
Probuilder: Seamless Level Design
There are already many popular Indie Game that are literally out at the market which was all specifically made with this same Unity toolset. Some of the games are "Tunic, Tacoma, SuperHot, Melon Simulator, Desync, Manifold Garden, Republique, Strafe, etc."
Developer Showcase:
Link: http://www.procore3d.com/showcase/
If you're interested in gaining access to this Unity toolset you can get straight from ProCore's main website here:
http://www.procore3d.com
Or you can download it straight from Unity Asset Store:
https://assetstore.unity.com/packages/tools/modeling/probuilder-111418
Back then Probuilder was once over $100 but now Unity Enterprise decided to give each of Procore's tool-set to Gaming Community for free in full version and that's just a tip of iceberg compared to what they're planning for the future. Anyhow I should at least show you different shots of "Medieval-Innhouse" that I had model within unity engine in greybox version which is also completely coated in vertex painting just to gain some sight of the possibilities this model could become.
Medieval-Innhouse:
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