Hi,
since one potential application for a single board computer would be to act as a terminal for online services. However traditional BBSes typically require a full-featured keyboard and 80 columns of text. Both are a bit hard to do on a single board computer.
Therefore I’d like to point towards the Videotex family of terminal standards. They were used for services like Prestel/Viewdata, Minitel or Bildschirmtext. There are different levels of support, with the simplest being like “Teletext” with pure text and block graphics, while others add user definable characters, photographs or vector graphics. Conceptually you can easily add full motion video and sound.
The minimal requirements are 40x24 text (so 240 pixel wide displays) and a “Telephone Keypad”. The user-interfaces are geared towards being used with those, at least for information retrieval.
A simple minimal client can be found here: