Houdini no longer has separate particle networks. The particle nodes are now in DOPs.
Channel nodes create, filter, and manipulate channel data.
Composite nodes create, filter, and manipulate image data.
Dynamics nodes set up the conditions and rules for dynamics simulations.
Object nodes represent objects in the scene, such as character parts, geometry objects, lights, cameras, and so on.
Render nodes either render the scene or set up render dependency networks.
Geometry nodes live inside Geo objects and generate geometry.
Containers for VOP networks.