if you mean free as in 'no money' then you will need to revise your list.
No Emb MCU is free. I mean, you are developping code using tools (are they at limited cost), do you need a simulator/emulator? what's the cost of ownership? can you distribute in volume? How steep is the learning curve? Time spent to port the core to your architecture? etc, etc .
Sometimes it's better to pay something for the license and in return you'll get a full blown design environment.