Its not completely freeware like Audacity, but has some incredible features. Ananda Ji and I have been testing with it, as one of its main features is doing a frequency sweep. We've found that by doing a 60 second sweep between 0.25hz and 6hz, we were able to very quickly find one or two "Delta Key" areas. Then we simply set the sweep for 60 seconds again, this time within 0.5hz to either side of the area we felt the most resonance. Then finally another 30 seconds or so within 0.10 hz to either side let us get right on the Key, to 0.01hz!
I noticed something else while doing this sweep...I felt a quick pulsing slowing down as I approached resonance (the Delta Key), and then right as the pulsing slowed to a stop, I had full body chills, so I knew when my Key was coming up. This is a much faster and more effective way of finding our Delta Key with this simplified system.
Another note, some of the audio files you are sharing in this thread take too long between frequency shifts. This is like playing a "disharmonic" note into your brain for a while, then another one, then another one, and it is not only uncomfortable, but ineffective. If you keep using audacity, please shorten your tones to 7 seconds or less... Even 1-3 seconds is enough for you to notice your resonant frequency (Delta Key).