Terrain Creator is a Blender addon for making terrains through a mix of procedural noise and hand-drawn features. Alongside the noise, you can draw terrain features like mountains and valleys directly onto your terrain for precise control over where they sit. A set of presets provides a starting point, including a temperate landscape, two desert varieties, ice, and a moonscape.
From there you can customize material colors and settings, add and adjust a water level with a generated shoreline, run water erosion, and scatter foliage. Foliage presets cover pine forest, temperate forest, tropical forest, cactus, and snow-covered setups, and you can bring in your own models by adding them to the custom_tree or custom_grass collections and selecting "custom" from the dropdown. A cutoff plane is also available. Material customization works in Cycles only.
The addon supports Blender 4.0 through 5.0 and is released under the GPL license. It comes in Full and Lite editions, with the Lite version leaving out presets and foliage scatter. Documentation and a demo video are available.