Your charger and the phone's internal circuitry should reduce the charge to trickle once the battery is full - just enough to power the phone. You'll notice that the charger will be warm while it's operating at full chat, but cools after that, indicating a lower level of activity. You don't need any additional software (such as a app). There's a debate over whether it's advisable to unplug the charger in these circumstances or not, but a lot of people do charge overnight with no apparent problems. If you're worried, the best thing would be a time switch set to run for 5 or 6 hours.
