Detail this asset from Unity Store: Original Link
This is a paid asset, but now you can download MeshBrush Free.
MeshBrush v2.0
MeshBrush v1.9
MeshBrush v1.7
MeshBrush is a Unity editor extension that allows you to paint meshes onto your GameObject’s surfaces.
Quickly detail and enhance the overall look of your scenes by directly painting your prefab meshes onto your GameObjects.
You can define multiple meshes to paint, how to randomly scale, rotate or offset them, and eventually change their size additively upon generation, without the need to actually modify any of the original prefabs.
Add multiple MeshBrush script instances to your GameObject to define several sets of meshes you want to paint, and adjust the randomness parameters for each set individually. MeshBrush will then cycle through your sets randomly and paint the meshes you defined based on the parameters of the corresponding script instance.
Once you are done painting meshes, you can optimize your scene by combining your painted meshes with the “Combine painted meshes” button.
When you feel like you have set up your perfect brush, you can save the configuration out to a template file and load it up in every brush you want. You can even share your templates with your teammates.
If you have any questions, feedback, eventual bug reports (I hope not… fingers crossed!) or anything else regarding MeshBrush, just feel free to contact me via E-Mail or post something onto the original Unity forums thread.
Also, if you want to share your interesting and awesome results with MeshBrush you can post them here into the official MeshBrush showcase forum thread.
Check out the official MeshBrush tutorial video on the Glitched Polygons YouTube Channel for more information.