So what happened? It's a terrible story, actually, as a fire put everything on hold for the developers. The good news is they're back at it and you can test Iris out for yourself. One of the things that makes Iris unique is its single-window interface (Image editors typically display palettes).
When you've got several images open, they're displayed in a row at the bottom of the window (see image above). It take some adjustment if you're used to a palatte-driven application, but nice and snappy.
Remember, this is a beta, so expect bugs and don't use it for mission-critical files. Iris will retail for $79 when it is released but can be pre-ordered for $39.