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