Elgg, like Idno supports a number of different views on data – standard HTML, JSON etc. However, unlike Idno, Elgg does not natively support JSONP.
JSONP allows you to make cross domain calls using JSON data, and is very handy for querying data from other sources using your fancy-pants javascript/jquery ajax code. It’s how, among other things, the idno feed widget running in the sidebar works.
Anyway, a commenter on another post asked about Elgg support, and because I had a few minutes spare, I put together a quick plugin!