The full editions of ProBuilder and Polybrush are now included as a part of Unity.
ProBuilder – a hybrid of 3D modeling and level design tools – recently became a part of Unity engine, allowing to quickly prototype structures, complex terrain features, vehicles and weapons, or to make custom collision geometry, trigger zones, or nav meshes. The tool is optimized for building simple geometry but capable of detailed editing and UV unwrapping as needed.
Polybrush, that is currently still in beta, can be useful to blend textures and colors, to sculpt meshes directly in the Unity editor and to scatter objects in the world with highly customizable brushes.
These tools are available to all Unity subscription plans through Assest store and – as ProBuilder – integrated in Unity 2018.1 beta.
For more info you can refer to Unity blogs.