WhatFont is a free App (IOS Only) for discovering the font used on a web page right from your mobile device.
Install WhatFont App from here.
Ok, so why would you want this App? If you develop software or design web pages, this App is valuable. Once you spot fonts on a web page, you can use them in your own designs. Once you know the name of the typeface, you are able to search and license the fonts. This App only works in Safari. No real magic here.
WhatTheFont from MyFonts is free (IOS Only). This App uses your camera or photos and scans for fonts using advanced image recognition. Like magic, this App works on everything from web pages and mobile app interfaces to real-world snapshots.
WhatTheFont finds the closest matches from their own database. From there you can purchase the MyFonts directly from within the App. They also have a forum that you can use to submit fonts that are not recognized.
Adobe Capture from Adobe is free (IOS and Android). Like WhatTheFont from MyFonts, this App also uses the camera to scan for fonts. Besides fonts, it scans for colors, brushes, patterns and more.
Adobe calls the fonts discovery feature Type. This App looks for matching fonts in Adobe's Typekit library where you can purchase directly from the App.
Because all three of these Apps are free, you could use them all (at least on IOS). You can also compare prices between MyFonts and Adobe for fonts you love and discover.