This is mainly an addon for Asset Forge 2 by Kenney (https://www.kenney.nl/tools/assetforge), but since the models are in OBJ format, you can use them in Unity as well. If you use ProGrids in Unity and tweak other parameters you can make stuff as smoothly as in Asset Forge, however, we recommend using Asset Forge and then exporting your creations to Unity once you're done, AF has some cool features out of the box that'll make your work more efficient and enjoyable.