When we install our software in exhibitions, we leave computers to be cared for by the gallery or museum staff. We configure the machines to keep them up and running autonomously. Thankfully, people are sharing knowledge. These posts by Blair Neal and Jan Vantomme lay out the basics for OS X and dig into some advanced techniques:

How to make an installation stay up 4evr (Mac OS X version) by Blair Neal

Configuring Mac OS X for Interactive Installations by Jan Vantomme

For those seeking to set up a video loop only, see:

Raspberry Pi Video Looper by Tim Schwartz