Dominik Lange offers a free, open-source SDF Modeling toolset for Side FX Houdini, offering a non-destructive, flexible way to model.
Modeling with solids is a great way to get organic and hard-surface forms without worrying about topology. An extension of the solid modeler is SDF or Signed Distance Fields. Unlike working with polygons, an SDF modeler sees the 3D space as a grid of voxels. For example, Substance 3D Modeler is an SDF modeling app, and so is MagicaCSG.
Thanks to Dominik Lange, you can now work with SDFs in Side FX Houdini. SDFModeler is a free, open-source SDF Modeling Toolset for Houdini that lets you work flexibly and non-destructively.
You can find and download SDFModeler here.