Garage Band
I’ll start with an easy one. For a free app that is included on your phone or tablet, it is extremely powerful. You can use this as a tuner or as a quick way to record yourself playing. It is really easy to use and a great way to hear how you have progressed.
Guitar Tuna
This is the best app for quickly tuning your guitar. It’s great for beginners because it only allows you to use standard tuning.
Ultimate Guitar
Ultimate guitar has been the go to site for guitar tablature and chords for years. The app itself also includes a tuner and a metronome and there are both free and paid versions.