There is lots of activity in the actually open source BeagleBone Black, especially in applications that need the PRUs.
List of compatible clones: https://beagleboard.org/logo
Recent Hackaday posts: http://hackaday.com/tag/beaglebone/
Be sure to check out the BeagleBone on a chip that was just released by a team of TI expats called Octavo.
Besides the SPARC cores you mentioned, the only other one I know of off-hand is the Propeller microcontroller core that Parallax released at DEF CON 22.
There is a raspberry pi project https://github.com/lanceseidman/PiCAST
And there is an android app I have seen used for this https://play.google.com/store/apps/details?id=com.bubblesoft.android.bubbleupnp&hl=en