This doesn't appear to have been updated since 2014, but I'd also add the now much more mainstream Seaboard to the list. It's somewhat more conventional, as it

This doesn't appear to have been updated since 2014, but I'd also add the now much more mainstream Seaboard to the list. It's somewhat more conventional, as it maintains the general shape of a keyboard, but that is an advantage in my opinion, as it makes it more intuitive to pick up and play while still offering a much higher degree of freedom over a traditional keyboard.