My New Year’s resolution was “This will be the year that I stick with learning the guitar,” so I don’t know how useful my list will be for someone who already knows how to play. It’s a mix of Android apps and mobile-friendly websites. I don’t mind paying to support developers and content creators but I do try to steer clear of subscription models.

• I’m using Justin Sandercoe’s highly-recommended online Beginner Guitar Course. There is a subscription-based mobile app but the web version is the same course and is free. I bought lifetime access to his Practical Music Theory course, which I’m taking at the same time.
• I’m using the Justin Guitar app without a subscription for the interactive Practice Exercises, which are not currently paywalled. Finger Stretching, One Minute Chord Changes, Scales, etc.
• I bought the Guitar Fretboard: Scales app for the excellent interactive Identify Note and Find All Note Locations training games in order to learn the fretboard.
• Under the Tools section in the subscription GuitarTuna app there is a Custom Chord Game I’ve found very useful. It’s a flashcards-style game which cycles through chords you’ve selected and challenges you to draw the chord diagram. Some chords are paywalled, so I’m looking for an alternative but haven’t found one yet.
• I bought the Functional Ear Trainer app in order to work on my tin ear. (I also downloaded Meludia Melody and Big Ear for ear training but haven’t played them much yet.)
• When it comes time to find songs to play I don’t have a great solution yet. To support the project I bought lifetime access to Chord Genome which allows you to specify chords you know and provides a list of songs supposedly containing only those chords. It’s a great idea and I think curating it using AI could be wild. But right now the site isn’t mobile-friendly, the database of songs is limited, and the chord information is only mostly correct.
• I use the Chord AI app to play along with songs found on YouTube. (Have a capo.) After buying the (expensive!) lifetime license in order to support the developer I was disappointed to learn that the Android app is missing functionality (like midi export) present in the iOS app. It’s currently my most-frequently used app, but I don’t know if in the long-term it will be worth what I paid 🤷
• After Googling the strumming pattern for the song I want to play I work on my abysmal rhythm using the Strumming Machine on Justin’s site. (I used 8Strummer the last time I tried to pick up the guitar, but it’s no longer supported on the newer versions of Android.)
• I previously purchased the now-unavailable lifetime license for the Songsterr app to play along with songs once I get beyond only strumming chords. For songs not in their database, Guitar Pro files can be uploaded. I think that TuxGuitar would allow conversion of midi to gpx but I haven’t tried it.
• I bought the TabFlow app, mostly to support future development. It plays Guitar Pro files in a Guitar Hero kind of style.
• I previously got into the Rocksmith 2014 CDLC scene and found this CDLC Player app. Unfortunately it doesn’t play the song, but a now-deleted fork did and I saved the APK here. RocksmithToTab seems to work for converting CDLC to gpx for using TabFlow instead.
• I bought a NUX Mighty Plug Pro headphone amp so when I’m playing along with songs I can get close to the sound of the original (and so my wife doesn’t strangle me while I’m practicing.) I use it with the FOSS MightierAmp app instead of the manufacturer’s app. I also purchased an M-VAVE Chocolate Bluetooth pedal which can apparently be used to control the headphone amp using the MightierAmp app, but it hasn’t arrived yet.
• I just bought Sheet Music Scanner because it was recommended here. I’m hoping to scan some obscure songs from song books then format shift from midi into gpx to upload to Songsterr and/or play in TabFlow.

Anyhow, that’s my list for now. I hope it helps someone.

Edit: I nearly forgot! Honorable mention for NewPipe SponsorBlock for allowing me to consume the countless hours of YouTube videos helping to supplement my learning journey without being inundated with ads.