proTile Map Editor 2 is a great tool for building various 3D/2D maps for your games and now with runtime support you can make building games.

Features

– Different brushes – mass placement, all snap, paint.
– Objects of any size – snap any tiles anywhere.
– Runtime support – Create runtime building games, full API for customisation.
– Tile-Connections – connect roads, walls and similar automatically.
– Custom Patterns – build once, place multiple times.
– Performance and size optimizations – combines meshes, reduces size for you.
– Layers – will help you to manage your maps.
– Easy to load and use – load maps in the editor, at runtime or stream dynamically.
– Procedural support – generate maps from code.
– Tile randomizer – Auto tile and rotation randomization.
– Different camera setups – Fits different 3D/2D type of games.
– 3D/2D Grid – Helpful visualisations.
– Custom Pivots – Setup Custom Pivot Scales and sizes, offsets.
– Terrain & 360 snap support – In alpha condition.
– Export Map – (or any other Objects from scene) to OBJ with textures and materials.
– Map Streaming – Stream map for seamless player experience.
– Editor for easy tile setup – categorise your tiles.
– All platform support.
– Open source, examples, documentation and much more!

(Supports Unity 4.6+ and Unity 5.3+)

Check out on the Unity Asset Store.