This is a paid asset, but now you can download Object Placement Tool Free.
Detail this asset from Unity Store: Original Link
Object Placement Tool v1.1 (Latest version)
Object Placement Tool v1.02
Object Placement Tool – it’s a powerful editor extention that allows you to populate your scenes in minutes using simple mouse click instead of regular drag & drop of prefabs and setting all rotation and scale variations by hand. The core feature of this tool is “Physics Placement Mode”. In this mode you can place your objects with the help of physics. You can easilly create huge amount of objects dropped onto each other, for example – the big heap of books like that shown in this video-demo
• Place objects on any surface by mouse click (or place only on selected object/layer);
• Physics Mode to drop objects onto each other and create big heaps of stuff;
• Randomize rotation and scale for created objects;
• Align to Surface feature to align created object’s up axis to the surface normal direction;
• Follow Path feature, place new object depending to previous object direction. Good for fence placing;
• Brush Mode to create objects by bunches;
• Group objects in the hierarchy or even combine meshes into a single mesh (works for meshes, that shares one material);
• NEW – Grid Placement, which allows to place objects as an array snapped to the custom grid.
3D-content shown in the video does not included.
P.S.: I’ll be very happy if you leave a review!