Thanks to Emilio for suggesting this topic for a flashback.

Before Softimage started shipping with Phoenix Tools ParticleSuite in 1999, SOFTIMAGE 3D had its own standalone particle system. If you wanted your particles in a SOFTIMAGE 3D scene, you had to follow this procedure:

• Render the SOFTIMAGE 3D scene within SOFTIMAGE 3D, using the SOFTIMAGE renderer with the Render Z Channel option selected in the Render Setup dialogue box.
• Load the SOFTIMAGE 3D rendered images into the Particle renderer as background images.
• Render the particle animation. Then composite the particle animation using the depth information from the z-channel of the SOFTIMAGE 3D rendered images to create seamless three-dimensional
  animation with a particle effect.

Here’s an overview of the SOFTIMAGE|PARTICLE interface (from the Particle User Guide) and a few screenshots of the viewport.