Comparison between model lines

I have the impression that Onyx has too many models, and I am trying to understand the main differences between them and their release cycle.

Looking over not only the current models, but also recent ones, what are the main product lines? Is there a regular release cycle, so that I can guess when the next one is coming?

(in the same way I can tell something for a ThinkPad from whether it is an X-something or T-something or an L-something, and that they are typically announced early in a calendar year)