Not perfect but got the job done well.

Lets all be honest here, you cant expect a perfect RTA from an iPhone or ipad, but this app does surprisingly well. I used this to ring out sound system in a large room with a basic mixer geq and pa amp. It was accurate enough to show me what frequencies were ringing and I cut them out using the geq. It worked well!

Radiofreq12 about Octave: An RTA for the iPhone