Every time you create an operator or press a button on the shelf you are executing a tool. In Houdini tools allow for everything from node creation, parameter modification and interactive viewport interaction to access to external pipeline elements.
Add custom attribute visualization to the viewport based on geometry.
Bubble Up network editor tool
Take a selected node in a Network Editor pane and swap it (bubble up) with the node connected to the first input.
Buoy object tool
Attach an object to a deforming surface like a buoy on the ocean.
Center the pivot of one or more objects to the center of one or more points.
Extract object pre-transforms to a parent null.
Collapse the selected nodes into a ForEach SOP.
Cone geometry tool
Create a primitive cone.
Extract each primitive group in an object to a separate container.
Convert spare parameters to asset parameters.
Match the world-space transforms of an object to another object.
Merge selected nodes in the current Network Editor pane together.
Apply radial forces on dynamics objects using a force field defined by metaballs.
Create a reference copy of the selected/chosen node.
Remove the pre-transforms of an object by moving them to the parameter transform.
Rocket dynamic tool
Create a system to self-propel a DOP object.
Connected selected nodes with a Switch operator.
Teapot geometry tool
Create a polygonal Utah teapot.
Transform geometry using a Transform Axis SOP about specific geometry entities.