We were in Grand Teton and Yellowstone recently and were thinking about taking tour buses until I came across a handy tour app of Yellowstone and Grand Teton combined for $9. No way I'll ever get in a crowded bus with strangers and be subject to a rigorous bus schedule when I can tour in my own vehicle and at my own leisure.
The I app I used is from a company called GyPSy Guide and it can be downloaded from either the Google Play Store or Apple App Store.
You download the app on your mobile device and you can connect the audio to your vehicle's sound system via Bluetooth or audio cable. The app does not need data or wifi to operate once is downloaded in your device. It uses the GPS in your device to know where you're located.
This is not some cut rate app developed by some kid in his mother's basement. The tour is narrated by a professional tour guide full of information about the specific area you're traveling through. I highly recommend using this app and ditching the tour buses.
GyPSy Guide