Yes, Parsec is independent software, working in the similar manner as other programs used for sharing desktop/giving control remotely. Basically you're giving some control to other person on your computer (in this case - to control second player). Good thing is, that the player who is "joining" you, don't need to own the game (he just controls, what he sees on your desktop).

Bad thing is, that such software can have problems with lag (shared video, reaction on control of player who joined you).
Don't know how well this Parsec works though, never had contact with this particular application. I would highly recommend to check if there is possibility to "limit" control to the person you're sharing the desktop (and to stop sharing it at any moment), to avoid unpleasant surprises.