Fine Tuner - Fine Tuner is a minimalistic guitar tuner that utilizes your device's built-in microphone.
Frontend Mentor - Supercharge your front-end skills by building in a real-life workflow. Solve real-world HTML, CSS and JavaScript challenges whilst working to professional quality designs.
MyGuitarTuner.com - Online microphone tuner for guitar, ukulele, violin and other instruments. Tune by ear or using the microphone of your device. It's fast and accurate algorithm makes it one of the best online microphone tuners available.
A Product Design Challenge - Get a design challenge to solve real-world problems
Metronomus - Powerful and beautiful online metronome
Singscope - See your pitch analyzed as you sing