I've tried Imagenomics' Noiseware software on the desktop, but generally find that the cure is worse than the disease: the over-smoothing effect it produces when trying to eradicate image noise from JPEG photos bothers me more than the noise itself. (Note that the Photoshop plugin which can indirectly work on uncompressed files is a different story and pretty good.) But I thought I'd give it a revisit on the iPhone 5S, since artifacts from phone photos tend to be even more severe. And if your mode of operation --like many people's -- is uploading medium-size shots to social networks for viewing on larger-than-phone screens, then it can be quite helpful at ameliorating ugly color noise, albeit at the expense of some image detail.
The interface is straightforward. You can process photos you've already shot or access the camera from within Noiseware. If you do the latter, you'll get the option to retake the photo or use it; if you choose to use it, you're popped back into Noiseware. That flow annoys me: I want to take a few shots, then process them. Also, I like the ability to save an original just in case. What if the next version of the product has vastly improved noise reduction? Then I can't reprocess an image I've shot with the app.
Once you've got an image loaded, you can choose from four presets -- default, weak, strong and a noise-reducing-and-slightly-brightening night shot. If you opt to make manual adjustments, the custom menu provides a toggle for severe noise and sliders for the intensity of the noise reduction and for brightening the exposure.