Check out 5 Unity packs with engines, toolboxes, and generators for environment creation.

Low Poly Terrain - Polaris 2020

Check out a cool low-poly terrain creation tool.

Features:

• Super easy to learn: Familiar workflow, no more guessing works thank to Live Preview, in-depth documents, or even get the answer right in the Editor before you have to reach out!
• Multi-threaded & GPU accelerated: Harness the power of Burst Compiler, C# Job System, and GPU calculation. Get instant results, in real-time. Multi-terrains editing handled with ease.
• Modern & easy-to-use toolbox: Complete toolset with some familiar and some unique you can't find anywhere.
• Advanced geometry generation: Speed up your scene with dynamic mesh wireframing, multiple levels of detail (up to 4 levels), Unity Navigation System compatible; more interesting geometry with cross-tiles matching, XZ plane displacement, holes, flat/smooth normal mixing.
• Massive foliage rendering: Dense forest rendered within a blink of the eyes with GPU Instancing, no Game Object overhead, billboard rendering & grass wind animation as well as interactive grass.
• Unlimited shading styles: From Lambert, Blinn Phong to Physical Based; from Gradient Lookup, Colormap, Vertex Color to Splats; whatever!
• VR ready: Achieve an immersive and high-performance VR experience in no time. Tested on Oculus Rift S.

Octave3D-Level Design

Grab a toolbox for environment building.

Main Features:

• Prefab categories and tags;
• Grid snapping;
• Object to object snapping;
• Easy prop placement;
• Prefab brushes;
• Object groups;
• Symmetry;
• Support for multi-story environments;
• Tile connections;
• Object selection;
• Single and mass erase tools;
• Snap and paint masks;
• 2D sprite support;
• Level optimization (mesh combine);

TerraWorld - Automated Level Designer

Check out a Unity plugin that will help you create a realistic environment using real-world data from ESRI, NASA & OpenStreetMap. 

Details:

• Detailed worlds using real-world elevation, satellite imagery & landcover data
• Natural Erosion & Terrace filters
• Outputs slope, flow, aspect & normal masks
• Advanced splat mapping & texturing
• Outputs water, trees, grass... regions from online landcover data
• Day-Night cycle with auto dynamic lighting throughout the entire scene
• Advanced Clouds Rendering with semi-volumetric representation
• Volumetric Atmospheric Scattering
• Volumetric Global Fog
• Volumetric Horizon Fog
• Global Procedural Snow
• Wind Simulation
• Water Shader with auto flow mapping
• Compatible with Unity’s Post Processing
• Automatic Lake, River, Ocean & Sea generation
• TerraMesh: mesh from terrain based on defined slope/height range
• Automatic Cache system to work in offline and faster iterative world generation
• No sign-up needed on external websites or sources

CScape City System

Create thousand of buildings in no time with CScape City System. 

• Advanced customized PBR shader with POM mapping helps to reduce the number of polygons while maintaining details.
• System for using simple building lo-poly template meshes, that can be customized in unity editor.
• Support for day-night cycling (animated in-house lights and building illumination)
• City generator
• All buildings use a sort of fake parallax interiors so that it gives an impression of complex meshes even in VR.
• CScape has an infinite possibility of customizations of building colors and textures
• A re-lighten feature that simulates night street-light for buildings and Ambient occlusion for daylight scenes (without the need to use costly lights or image effects)
• System for generating facade style textures in an easy way
• LOD system that automatically optimizes object details based on distance from the camera.
• Various object array systems help you put arrays of objects on building sides. -Rooftop system -Soon to come: Building Styles Packs, like Sci-Fi city, ’20’s New York, Italian city, Cartoon City, Apocalyptic City, Soviet City. The first version includes a pack called Megacity, capable of generating thousands of different materials with a single shader.
• CDK (content development Kit) for artists that want to make their own CScape Styles (and eventually sell them on asset store).

Terrain Grid System

Have a look at an advanced grid generator for terrain and 2D grid. 

Features:

• Easy to use. Add Terrain Grid System script to your terrain, game object or group of objects to instantly attach and configure the grid. Or drag & drop the prefab to use it in stand-alone mode (no terrain mode).
• Configurable, fully interactive, and fast grid generation, including Voronoi tessellation, box/squared, rectangular and hexagonal types.
• Compatible with Unity standard terrain, mesh-based terrains, or any game object with a mesh.
• Change visibility, color, or texture of cells from Unity editor with the integrated grid editor.
• Produces highly optimized grid mesh with reduced vertex count.
• Two levels of regions: cells and territories.
• Fastest selectable and highlighting system for both cells and territories.
• Coloring and fade-out support for both cells and territories.
• A* Pathfinding for boxed and hexagonal grids with customizable cell weights and obstacles.
• Easily define blocking cells or assign cells to different groups (zones, obstacles, custom navigatable paths, ...)
• Get neighbors or cells in range according to crossing cost, max steps, or cell group masks
• LOS (Line of Sight) functions.
• Easy rectangle selection of cells.
• Different positioning options for best mesh adaptation to the terrain, including scaling and positioning inside terrain boundaries, maximum terrain slope, minimum altitude, ...
• Control the visibility of individual cells using API or alpha texture mask.
• Define territories using a color texture or the embedded grid editor!
• Supports multiple grids in the scene as well as multiple grids per terrain.