Software like Antares Autotune Live keeps you in tune but as commenters noted too, it might be more useful to study to get your technique better.
If you'd just like to see how far you're off (for practicing purposes as an example), it could be an idea to get the Reaper DAW (http://reaper.fm/). This DAW comes with a plugin named "ReaTune" and will display exactly what note is being sent into it, along with how much you need to go up or down:
Since the people that produce Reaper have a really nice policy on being able to use their product without paying for it, it might be an idea to try it out. It will most definitely help you in improving your vocal technique.