I've built a good ol' web app which runs in fullscreen mode on an old iPad 1, turning it into a "smart" picture frame. Runs on top of Trello, with a small backend in Go for caching and proxying. Works great.
I do intend to release it and also open-source the code at some point. It's not entirely in that state yet, but I'll probably throw it up on a Show HN when the time comes.