I just published my first package on the Unity asset store. It’s called Polygon Reducer, and it reduces the vertex count of meshes in real time, as you drag a slider.
It works both in the editor and in play mode, supports all things I could think of (animations, submeshes, etc.) and even some things I didn’t know would be an issue such as seams in the mesh, where vertices are joined together but not connected by a triangle.