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.
Befront - Learn UX/UI design skills in practice with bite-sized tasks
Fine Tuner - Fine Tuner is a minimalistic guitar tuner that utilizes your device's built-in microphone.
UX Challenges - Done reading about UX? Start doing it.
LINGOT - Musical instrument tuner, LINGOT is a musical instrument tuner.
Weekly UX Exercise - Receive challenges top companies use to interview designers