For a “limited time”, this tuner app is free. It has many different turnings for guitar, banjo, mandolin, etc. I’ve used it a few times, and it seems to work OK. Normal price Is two dollars, not sure how long it will remain free.
Tuner app for ipad/iPhone
Amazon has an mp3 sampler album for free called “bluegrass mastery volume 1”. Get it while its free!