I was beta tester for WireTap Anywhere and know a little bit about the app.
WireTap from Ambrosia Software comes in two flavors, "WireTap Studio" and WireTap Anywhere". They are more like audio utility application like "Audio Hijack" (another great app) which provide features and functionality that are not available in OSX.
GarageBand is a DAW (Digital Audio Workstation) like Logic and ProTools, a different kind of app.
I used WireTap Anywhere with Logic as a plugin (one of the first 64bit AU plugins available). You could route the audio output of any app (i.e.Safari, iTunes) directly into Logic and record it. Or tap the audio in and out of any connected hardware audio interface and route it to Logic to record a skype phone call for example. WireTap Studio has a few "DAW-like" features to record and edit audio but for specific purposes and is not an all around multitrack recorder/sequencer.
GarageBand supports AU plugins so you could use it, but there is one catch. OSX Lion changed the underlying code that WireTap was based on. Starting with Lion, the OSX code imposed some major restrictions how applications can communicate with other applications "under the hood".
Until today the developers haven't figured out how to come up with a solution for that lock-down to provide the same pre-Lion functionality for WireTap. Too bad.
Hope that helps
Edgar Rothermich