Nucleo is a plugin which speeds After Effects performance by using multiple processors or processor downtime to for preview and background rendering. From the Features:

Fast (Nucleo) Render
Supports rendering out to both sequences and movies in any format supported by After Effects.

Fast (Nucleo) Preview Emulation
Allows you to specify which type preview you would like Nucleo to emulate, Standard (spacebar) Preview, RAM Preview, or Shift RAM Preview.

As you create your composition Nucleo automatically and continuously renders it and fills in your AE RAM Cache. When you make a change Nucleo detects it and regenerates the frames.

As you create your composition Nucleo automatically and continuously renders it in the final output format. When you make a change, Nucleo detects it and regenerates the appropriate files.

Background Render Queue
When you render using Nucleo’s background render queue, you can continue to work in After Effects, or any other application. Load the background render queue up with compositions from several different projects and Nucleo will let know when they have completed.

Commit To Disk
If you have layers in your timeline that are complete but are costing you time when previewing, Nucleo allows you to commit those layers to disk. Simply select the layers and have Nucleo render only those layers out in the background. When the render is complete, the selected layers in your composition are non-destructively replaced with the rendered footage item.

CreativeCow’s Aharon Rabinowitz has posted a video review, outlining some techniques and a couple of his issues with the system. Anything which can speed your workflow and reduce rendering downtime is fantastic. $495 is a little hefty for the independant VJ, but if you’re doing freelance post or video production the time it saves may be worth the dollars.