The Sceelix Unity plugin, as provided with Sceelix itself, updated and extended for use with Unity 2019.4 and up.
As of Sceelix v1.0.0.0, it's open sourced (see https://github.com/sceelix/Sceelix), but there are numerous bugs and corner cases, some annoyances, some more serious. Especially with some changes in Terrain handling in newer Unity versions needed work.