BuiltWith - Find out the technology behind websites
Fine Tuner - Fine Tuner is a minimalistic guitar tuner that utilizes your device's built-in microphone.
Wappalyzer - Wappalyzer is a technology profilers and leads data provider. Create lists of websites and contacts that use certain technologies.
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.
What CMS - WhatCMS.org looks at a variety of factors within a webpage to determine what CMS a website is using.
Metronomus - Powerful and beautiful online metronome