Groove is a Canadian-made mobile app that’s tearing up the charts, reaching a top 1o spot in over 30 countries, and climbing to number 1 in the Canadian app store over other music apps including Rdio and Songza. The app is part of Montreal-based FounderFuel‘s latest cohort, and in move that’s becoming a trend for Founder Fuel companies, it has just gone free, and racked up 85,000 downloads in just 24 hours.

Going free is bound to generate interest, but for FounderFuel General Manager Ian Jeffrey, it’s an especially effective tool for some startups that have the potential to gain some amazing early traction but might be too focused on revenue early on. The Transit App, another FounderFuel company, recently went free and amassed an amazing 35,000 downloads over the course of just 72 hours, but Groove’s uptick in interest is even more impressive.

“Free is not necessarily always the way the go, but in both cases here it made sense,” Jeffrey told me via email. Of course, that’s bound to raise the question of whether or not going free is sustainable in the long term for these kinds of apps, and others like them hoping to make a splash in their own respective categories. Whatever the case long-term, the fact is that it seems like these apps stand little to no chance getting a good head of steam going without at least trying the free route first.

Groove is different from other playlist apps like Songza and 8tracks in that it uses your own library to populate content. That’s simpler from a licensing standpoint, and also lets a user rediscover content they already own and may have long forgotten about. Plus, it not only automatically organizes your music based on your own listening tastes and tags, but also can pair up with friends to combine tastes, which is perfect for setting the mood at parties in a way that hopefully pleases everyone.

So far, the app has amassed over 1 million downloads in the App Store over the past two years, but now it’s growing at a much faster rate. Free is the draw, and seems to be the difference between limping along and really spiking, but long-term we’ll have to see how these companies adapt to the changing economics of the App Store to build a lasting business.