The study items are listed on the Open Source CPUs post, especially the category description.

Let’s have a look at OpenCores Certified processor Projects.
OpenRisc1000 is already done.

openMSP430

This is a clone of TI’s MSP430, a 16bit micro-controller. Just by this it’s a tiny micro-controller again…
Also it’s a clone again, there is a port of GCC for the MSP430 family: mspgcc.

Plasma

This on is a Mips-like, that is to say it has most MIPS I instructions except the patented one (the page says the patent expired, so one could probably add them, need to check the legal stuff, remember I’m no legal expert).
Well it work, is still serving a website so great 😉
It does not look like there is any MMU, so it’s an embedded CPU.

T400 µController

An implementation of a legacy cpu again… clone of National’s 4-bit COP400 microcontroller.
The distribution include a GPL V2 text but the header in the vhdl files does not refer to GPL but gives a rather more permissive licence (looks BSDish to me) especially allowing synthesized work to be distributed without the source…
As for the category, it’s a 4bit cpu remember, so a tiny micro-controller.

T48 µController

This is a MCS-48 microcontroller clone. The licence is the same as T400 above (it’s the same author).
A 8bit micro-controller that will continue to flood the tiny micro-controller category.

As usual the summary table is there: Open Cpu Study Summary.