Meet ExtensionFM, the Music Start-Up Google Should Buy

You’re going to have to wait some time before you can use Google Music, because the service doesn’t exist yet. But if you want a sense of what it should look like, go play with ExtensionFM, an interesting start-up that plays off Google’s Chrome browser.

In a nutshell, ExtensionFM allows Chrome users to temporarily store, and play, most music they come across as they tour the Web. There’s an explanatory video at the bottom of this post, but the easiest thing to do is simply fire up Chrome, add the service to your browser and go surfing. You’ll be particularly happy if you visit MP3 blogs and Tumblrs.

The problem for Dan Kantor’s New York-based start-up is that, for the time being, it’s got a limited number of potential users. Chrome has less then 10 percent of the browser market, and only a subset of those users are comfortable with the idea of adding “extensions” in the first place.

Perhaps that’s why ExtensionFM has just 25,000 users after launching earlier this year–even after Google (GOOG) gave it a boost by featuring it at its I/O developer conference. But Kantor, who has put in time at various start-ups–most notably Delicious–as well as at Yahoo (YHOO), Microsoft (MSFT) and AOL (AOL), says he plans to expand to other browsers–Apple’s (AAPL) Safari browser just got a lot more extension friendly–and eventually the service will move onto mobile platforms, etc.

That’s the bet, at least. Kantor has raised a seed round from high-profile investors like Spark Capital and Betaworks, so they’re expecting this thing to move on from ultra-niche status eventually.

Or Google could just buy the thing outright and plug it into whatever it does launch, whenever that happens.

In the meantime, here’s a recent sit-down I had with Kantor:

And ExtensionFM’s own description of its service: