Artistic Techworks - Audiodia v1.0.6 (Mac/Universal)

From the homepage:
Having fun with real-time audio filters.
Audiodia is a real-time sound processing application. Simply turn on your microphone and your speakers, select the desired audio filter and press Play or Record.
Audiodia is fully bilingual — it will run in English or French, depending on your system's language.
Audiodia gives you access to the AudioUnit filters that ship with Mac OS X, such as the Reverb and the Delay filters. It also ships with a built-in pitch-shifting filter. Audiodia lets you pick favorite filters and quickly switch from one filter to another during use. The sound output is mixed with your other applications' sound output, so you can add your voice over music playing in iTunes, for instance.

Audiodia is especially useful for:
Disc Jockeys
D.J.'s looking for new ways to entertain people will find plenty of things to try in Audiodia. Mac OS X also ships with a variety of nice filters such as a Reverb, a Delay and more.
Making Presentations
Are you using your Mac to make presentations? Add in a microphone, speakers and Audiodia and you can control both the audio and the video from your Mac.
You can use Audiodia to sing over music played in other applications. You can even fine-tune the mix by adjusting the volumes independently in each application.
Having Fun with Sound
Audiodia gives you access to the AudioUnit audio filters installed on your Mac, and it also includes its own pitch-shifting filter. Have fun!

Price: 15 dollar