pynuts
A unit conversion tool in Python, mostly written as an exercise rather than to provide anything that's both new and useful.
Commandline interface
$ python -m pynuts 'km/s * h/yd'
3937007.87402 (1)
$ python -m pynuts mm/ftn --to yd/h
3.25480148315e-06 (yd / h)
$ python -m pynuts '50 in' --to cm
127.0 (cm)