TerrainComposer and WorldComposer create standard Unity terrain and they are compatible with anything that is compatible with Unity terrain.
Here are products that I recommend:
Relief Terrain Pack V3
I’m collaborating with Tom from RTPv3. TC has integration to set RTP up more quickly for splat textures and multi terrain tiles. RTP is the most advanced terrain shader on the Unity Asset Store. You can adhieve amazing results and it has many features like snow/water/mesh blending. RTPv3 is used in the TC2 trailer.
Horizon[ON] will make your Unity terrain/s or mesh terrain extent towards the horizon and makes your terrain look huge with very low performance cost.
World Streamer slices your Scene into smaller Scenes with the click of a button and will stream those from the disk. TC2 has streaming but for everything that is generated and placed by it. But if you placed things manually in your Scene you still need World Streamer if you really want to stream it into memory.
Time of Day
Time of Day is a package to render realistic dynamic sky domes with day and night cycle, realistic celestials, dynamic clouds and physically based atmospheric scattering. Time of Day is used in the TC2 trailer and we also use it in our game.
Map-ity is compatible with WorldComposer to add real streets meshes and 3d buildings using Open Street Maps.