Stop operator:
Normally in Particle Flow, when you want to stop particles, you need to add a Speed or Spin operator (or both) and then set their values to 0. Now you can just drop the Stop operator in a new event, and voila: particles stop completely as soon as they enter the event. The operator has check boxes for Position and Rotation, so you can choose to stop linear motion or angular velocity, or both if you like.

Stop Gradually test:
This test builds on the capabilities of the Stop operator, letting you stop particles gradually. You can set the time at which particles should begin slowing down, as well as the time at which they should come to a complete halt. Both times can be synchronized with the entire animation, or particle age, or event duration, and you can vary these times randomly as an option. Because Stop Gradually is a test, when particles are completely stopped, you can redirect them to another event.

Camera IMBlur operator:
The operator is intended for use when rendering a particle system with motion blur as viewed from an animated camera. It corrects a problem in which Image Motion Blur doesn't take camera motion into account when rendering a particle system. The operator adjusts the particle speed, accounting for camera motion, before it's passed to the viewport display and/or the renderer.