Well, as I have found, there is the DIY way, as done at Uinversity of Minnesota and Purdue:
Biology's Digital Sign Project - College of Science IT Wiki
One trick - Use Apple Remote Desktop to monitor, an Applescript to run the Keynote presentation.
Applescript Forums | MacScripter / Using Keynote as a Digital Sign / Kiosk
Depending on the display, you may need this:
And then there's the commercial way, just announced this summer:
Still looking for other options.
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