JACK audio recorder for spontaneous and conservatory use.
Download it here.
I use it very often to capture Rosegarden output and to convert in WAV format, before encoding it with Oggenc or Lame. It writes WAV files with a sample format of 32bit float, which is not appropriate to my configuration. So I must use Rezound to transform it to a signed sample format with a sample width of 24.
You can capture all that Jack can manage. It is especially great when you just want to grabe what actually sounds on your soundcard (audio CD, sounds of video DVD...).
$ ./configure --prefix=/usr $ make $ su -c "make install"