Hindu Navgraha Mantra Android apps including Hanuman and Gayatri Mantra is created by Dilip Bhatt. The Apps are available on Google Play. These are paid apps and are not free.
The author of the apps claim:
The apps come with a soothing audio clip of the mantras and is pronounced exactly the way the Vedic Rishis have suggested it to be done. You would be able to pronounce the mantra exactly without any mistakes, just as a learned Indic or Vedic scholar would.
The repetition is traditionally done in a set of 'number presets' (usually 7000 times for Sun God) that is usually thought to invoke the right amount of energy sustainable by the human mind. The application comes with these preset numbers that can be selected depending on how much time you have to spend during each session.
You can get more details about the Navgraha Mantra apps and how to download other details here.