CoCoIOr features the WizNet 5100s ethernet chip. This device can manage 4 separate TCP or UDP network stacks all by itself, the host computer's job is to feed those pipes. Works with CoCo 1, 2, or 3.
This is the original serial/network version, missing it's 16550 serial UART. If you want to experiment, here's the thing. We even have a serial driver for OS9. For everyone else, there is a newer version of this product, see 'CoCoIOr' on this same product page.