[qi:gigaom_icon_cloud-computing] Heroku, the San Francisco-based startup that offers a Ruby-focused cloud platform as a service, last week saw the number of apps deployed on its platform top 40,000, according to CEO Byron Sebastian. He joined the company after stints at BEA, EMC (s emc) and most recently, SourceLabs, where he replaced co-founder James Lindenbaum as CEO. Heroku, which offered its services for free during its beta, started charging for its platform back in April. Sebastian stopped by our offices to give us a quick update on the state of Heroku.

Heroku is adding about 1,000 apps to its platform every week and sales are growing at a rapid clip, Sebastian told me. But he declined to share any revenue specifics, despite my repeated requests, which tells me that they’re still a ways off from being meaningful. Indeed, the company’s low-cost platform first needs to scale. Sebastian, however, remains confident: “We see a lot of new apps go live with small app development and testing…but in couple of months people shift to premium models.” The 2-year-old company was incubated inside YCombinator and raised about $3 million in funding from RedPoint Ventures and certain individuals in May 2008.

According to some developers who are currently using Heroku, the service hits a sweet spot of “managed application hosting at a reasonable price point (and with free small-scale deployment).” Add to that its ease of use, and the gushing of such developers over the service makes complete sense. It helps that Heroku has been listening so intently to the developer community and has subsequently been rolling out some of their most-requested features. For smaller developers, the low entry price is definitely a differentiator. But while the company has targeted its service to the developers of Facebook and iPhone apps, it’s slowly seen interest emerge from larger enterprises. “We are seeing a transition from being a prototype platform to being a platform for serious business apps,” said Sebastian.

Heroku’s platform is based entirely on Amazon Web Services (s amzn) such as EC2 and S3, which allows the company to lower its initial capital outlay while at the same time enabling it to scale as needed, depending on its end customers. As Derrick Harris previously noted, Heroku’s platform-as-a-service offering makes deploying web applications “a trivial process, where developers can forgo the busy work of configuring app servers and databases, and of allocating resources to each component.”

Heroku’s recent growth spurt mirrors that of cloud computing services, especially those in the U.S., many of which Derrick wrote about in a recent note for GigaOM Pro (subscription required). I’ve been hearing similar stories as to the robust demand taking place across the cloud ecosystem. In the meantime, AT&T (S t) last week started offering a cloud compute service and Microsoft (s MSFT) is getting ready to launch its much-awaited Azure cloud offering early next year.