there are several clip on tuners .. intelli is one, intellitouch is another..there are several....they tell you what note is being played and tell you if you need to tighten or loosen the string to get it to the tone you need.

there are also several online tuning helpers...
one that generates a tone and you can match that note with your instrument ....
others can "hear" the note you play, and let you know what you
need to do to get it on tune...tune up or down...

try this...http://www.get-tuned.com/online_instrument_tuner.php
or this: http://www.onlinetunermetronome.com/

your computer will need a microphone or speakers for these.