LogicLike
Brain Games
Dualnback.works
Pixelogic - Daily Picross
Mathly
LeveLisa
Hue Brain Games
Ecovolife
Uberchord Guitar
Fretello
Justin Guitar
Guitar Pro 7
Fretuoso
Go PlayAlong Tab Player
Moosiko
Guitar Trainer
LogicLikeI've been using Uberchord for a few years by now and it's just amazing. It's all about chords, rhythm and songs. This is no child's game, though, you actually learn how to play. The recognition works for most of my guitars and is borderline crazy, even showing me if I put a finger on the wrong fret. It won't let you just play anything and still pass. They have courses library (they call it learning path) and a pretty large catalog of popular songs. I wish they had solo training, but all in all, highly recommended.
Brain Games - Boost memory power with free brain games
Fretello - Duolingo for learning how to play guitar
Dualnback.works - Dual N-back is a specific brain training exercise, that's been shown by research - it might improve fluid intelligence.
Justin Guitar - Over 750 completely free guitar lessons!
Pixelogic - Daily Picross - Nonogram logic game with 5000+ puzzles and a daily puzzle
Guitar Pro 7 - Create, play and share your tabs