Mantis LOD Editor – Professional Edition

Mantis LOD Editor Pro is a complete mesh simplification solution(Include an editor extension, a batch generator, a command-line utility, a standalone app, and a progressive mesh runtime).

You can simplify your meshes and make LOD from within Unity’s editor, from the standalone app, or from the command-line tool.
The toolset can generate high quality LOD with extremely low triangles count, this is very important for mobile games.
This product can run on Windows x86_64 and macOS.
This product contains advanced progressive mesh technology for Unity.
What’s progressive mesh technology? It is an advanced automatic LOD technology, you no longer have to make LOD manually.
Generated progressive meshes support all platforms, make once, run anywhere.
This product supports Unity 2018.4.0f1 and newer versions.

Features:
Provide source code, you can modify the source code to fit your need.
Generate LOD for static meshes and skinned meshes.
Protect UV boundaries and material boundaries automatically.
Protect open boundaries or smartly merge some smooth parts of open boundaries.
Preserve all blend shapes.
Super fast, it can simplify 50,000 triangles per second.
Preview final effect in real time.
You can simplify huge 3d models with the standalone app.
You can write shell script to simplify hundreds of 3d models with the command-line utility in batch.
Advanced progressive mesh technology.
Generate progressive meshes for hundreds of 3d models in batch.
Supports vertex color map(Red channel) as detail map, control which area should have more details accurately.
The progressive mesh runtime supports XR.

Here is the introduction video:

Here is the latest video tutorial:

You can find the plugin’s source code at ‘Plugins/Managed/MantisLOD.cs’, the plugin calls the DLL version by default, for it is much faster than the C# version, you can edit ‘Common/MantisLODEditorUtility.cs’ to switch the plugin version.
The latest version supports vertex color map(Red channel) as detail map.
You can paint vertex color map with your favorite tools, then use the vertex color map(Red Channel) as detail map to control which area should have more details accurately.

https://assetstore.unity.com/packages/tools/modeling/mantis-lod-editor-professional-edition-37086