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Uberchord Guitar - Get better on your guitar. Fast.
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