I am in need of a free tone generator (enter a frequency to output) for Mac OS X that can be "dialed" in real time. I need to be able to adjust a slider without having to stop/start/type in a new value. I have not been able to find a single application that can do this.
Audio Signal Generator by Bill Farmer, GPLv2 licensed.
It doesn't have a "slider" per se, but its knob dial might just be enough.
If you want something more complete and don't mind parting 5 USD, AudioTest from Katsura Shareware is also very usable, with a slider.
Here's a tone generator / tuner application that I wrote, available for free online:
It was originally to help people with tinnitus find the frequency their ears are ringing at, but it certainly has other uses.