harmonizer.lv2 uses the aubio toolkit for note onset and pitch detection on audio input and outputs midi.
Compiling harmonizer requires the LV2 SDK, bash, gnu-make, and a c-compiler.
git clone git://github.com/dsheeler/harmonizer.lv2.git
cd harmonizer.lv2
make
sudo make install PREFIX=/usr
Note to packagers: The Makefile honors PREFIX and DESTDIR variables as well as CFLAGS, LDFLAGS and OPTIMIZATIONS (additions to CFLAGS).