This is a paid asset, but now you can download TerraTex – Automated Terrain Texturing/Splatmap Free.
Detail this asset from Unity Store: Original Link
TerraTex – Automated Terrain Texturing Splatmap v1.5 (Latest version)
NEW Lite version is now available for free here
An automated script to texture Unity Terrains based on a wide range of configurable parameters.
Very easy to use, much less complicated than other tools with a user friendly interface and design
Includes customisable layers, with the option to use up to 12 textures for each, and several options for the distribution and blending of these textures.
Customisation options include, though are not limited to: sea level, snow altitude, cliff steepness & texture perlin configuring.
With this you can create virtually any terrain you want in just a couple of minutes – whether it’s grassy, rocky mountains, dessert, volcanic, glacier etc.
Check out the screenshots and videos to see what this tool can do with ease.
A demo scene is also included with an already generated texture that you can adjust the settings for to see the effect
The texture can be generated from a button click in the editor and can also be previewed live as you update the settings
Documentation for more info