Terrain Former

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 mutliple 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.
Note: Details (rocks, grass, etc) and trees tools are planned but will be coming in a future release of Terrain Former. You can however in the meantime, easily switch between Unity's terrain tools and Terrain Former.
Official Site
Roadmap
Documentation