Download Terrain Former FREE Unity. 

Terrain Former is an intuitive and simple terrain editor for Unity with support for multiple terrains, allowing for terrains suitable for even the biggest open-world games.

Features:
– Full multi-terrain support—sculpt seamlessly across multiple terrains.
– Raise/Lower,
– Grab
– Smooth,
– Flatten (with Bridge, Extend modes),
– Set Height,
– Paint Texture,
– Heightmap Importer, Heightmap Export to EXR,
– Mould (formerly Shrink Wrap),
– Generate—generate terrain that follows a curve (w/ linear and circular modes)
– Terrain Grid Creator Wizard,
– All tools work across terrain grids

Terrain Former addresses all of the major issues with Unity’s built-in terrain editor, such as the painfully slow smoothing tool and its constrained brush size.