RPI's running something like plan9-bcm (check github) where gpio is exposed should work. I'm going to try plan9-bcm this weekend; i'll keep you posted. I like ODROID hardware, but obviously there isn't a Plan 9 port for it.

Arduino Yún (MIPS+AVR) could make a cool device for Plan 9, but the MIPS part of the hardware is closed.

On the smaller end of the scale, I've just started porting lib9p to esp8266. I'm using ESP01; it is a cheap yet very capable device.

On Wed, Aug 5, 2015 at 1:39 PM, Brian L. Stuart <blstuart@bellsouth.net> wrote:

I'm teaching a special topics course this fall I'm
calling Computing in the Small. Right now, I'm
leaning toward conducting it on a platform that
runs Plan 9. I'm looking for something based on
ARM or MIPS and that has some useful connection
to the external world in the form of GPIOs. SPI,
I2C, and analog I/O would be nice to have too.
Obviously, the Raspberry Pi is a candidate. What
are some others? I've seen some code in the
source tree for the BBB. Has anyone tried it out
to see what is and isn't there? How about the
Banana Pi? The SATA port on it is quite appealing.
Some of the other options I've been looking at
include the VIA APC Rock and Paper, the Phytec
Cosmic, the CubieBoard, the Odroid, the Riotboard,
and the Wandboard. Has anyone done anything
on porting Plan 9 to any of them? Are there others
I'm missing that would be good targets for such a class?

Thanks in advance,
BLS