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Web Morse player is exactly what the name says: a Web app that encodes a text into Morse and is capable of playing "dit-daat-daat" audio. Page is https://epxx.co/morse/.
There are many other online apps like that in the Web, based on Java or Flash or whatever. The thing that makes this app different is the employment of HTML5 Audio API.
This API is not widely deployed yet; the only supporting production browser (that I know of) is Chrome, and you need to activate it in about:flags page. It inherits implementation from WebKit, so other browsers like Safari are expected to offer this feature soon.
Being experimental means that Audio API could make your browser unstable etc. The only problem I noted is some audio interference and clicks when browser is doing some other processing, like scrolling page, opening another tab etc.
High-level Morse code is based on PaiMorse. Sound quality is more or less the same as CoreAudio backend of PaiMorse, even though Web Morse uses a simpler form of playing sounds (scheduling pre-calculated sound buffers) while PaiMorse with CoreAudio generates audio in real time. (Audio API supports the latter too, so we can change that to get better quality in high WPM.)