Systolic arrays often (always?) have a predefined communication pattern and are often used in problems where data that passes through them is also retained in some shape or form.
For NextSilicon, the ALUs are reconfigured and rewired to express the application (or parts of) on the parallel data-flow acclerator.
GreenArray processors are complete computers with their own memory and running their own software. The GA144 chip has 144 independently programmable computers with 64 words of memory each. You program each of them, including external I/O and routing between them, and then you run the chip as a cluster of computers.
One distinction of the GreenArrays chip is that they claim it is very energy-efficient.