Google Chrome extension allowing you to scrobble to Last.fm.
Available on Chrome Web Store: https://chrome.google.com/webstore/detail/iepmcfkedcobclgjlblahmlekodmnmmk

Project released under MIT license.
Project icon got from iconspedia.com (under CC Attribution Share Alike license).

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Application splits into two parts: front-end and back-end.

Front-end

Front-end presented by connectors. Connector is the JS code injected in webpage to observe player events or user actions. Content script injector.js decides which connector to inject based on window.location and it's own CONNECTORS map.

Connector must notify back-end when track starts or continues to play by calling sendToBackground function.

When track starts to play, connector must define it's id (it may be number, string or even just full name of track) and call:

sendToBackground({
    event: 'start_playing',
    song: {
        id: <id>,
        duration: <duration in seconds>,
        artist: <artist name>,
        track: <track name>
    }
});

Every LASTIQUE_UPDATE_INTERVAL_SEC seconds connector must check and send continue_playing if song continues to play:

sendToBackground({
    event: 'continue_playing',
    song: {
        id: <id>
    }
});

Back-end

UI developed using Hogan.js -- JS templating engine from Twitter. Chrome's Content Security Policy disallows "code generation from strings" (eval(), new Function), so that Hogan.js templates can only be compiled in sandbox. It seems too complicated, so I chose to precompile templates instead.

Run ./compile_templates.sh -- it will compile templates and update compiled_templates.js. It requires node.js with Hogan.js installed (npm install hogan.js).