Prefab Summoner can help you to easily populate your scenes with lots of gameobjects or place single instances painlessly without having to constantly duplicate and move a gameobject with the standard tools. It does not require a Unity Terrain. Mesh optimization is also integrated to reduce draw calls and improve the game's performance. Get it at a lower price for a limited amount of time!

Some Features:

-Compatible with versions of Unity 4 and 5.
-Easy to save your settings. Just make a prefab out of your Summoner.
-Optimize your gameobjects into chunks/octrees with the ability to also preview them and reduce your draw calls with a single click.
-Customizable keys.

-Single Mode
-Supports scaling, rotating and moving objects fast.
-Place on a Grid option, without any object.
-Use Surface Direction
-Mass Delete and Precise Delete Brush
-Clamping options.
-Snapping options.

-Multiple Mode
-Summon lots of different prefabs at the same time.
-Randomize rotation and scale with global options or different for each prefab.
-Use Surface Direction
-Mass Delete Brush
-Avoid overlapping objects, if you wish.

Forum Link https://forum.unity3d.com/threads/prefab-summoner-fast-and-efficient-gameobject-placement.446566/
Send suggestions/bugs: liquidfiredev@gmail.com