Archive notice: This article was originally published on March 21, 2013. Links and embedded videos are preserved as part of the historical record.
In principle, NukeX Assist is a seperate NukeX licence with restricted functionality. However, it is not offered as a standalone product, only as part of the NukeX licence. Two Assist licences can be ordered free of charge for each NukeX licence.
According to The Foundry, Assist gives artists access to a selection of Nuke nodes, allowing work such as Paint, Roto, 2D Tracking and Planar Tracking to be delegated to assistants. Unfortunately, Assist is not available to Nuke users and is included as a feature only with NukeX licences.
Additional functions in NukeX compared with Nuke include a 3D Camera Tracker, 3D Particles, Planar Tracker, Denoise, GPU Acceleration, ModelBuilder, Lens Distortion Tools, Modelling and Point Cloud Generation, as well as Pixar RenderMan Pro Server support.
You can find all further information, and when the the NukeX Assistant will be available, here.