Yammer, originally launched as a “Twitter for businesses,” will soon expand its services into a full-on social network like Facebook — built to help streamline workplaces and network business professionals.

Along with a redesign to be more social, the Yammer developers are also providing access to developers in order to attract third-party apps. Yammer is also going to allow for event creation, threaded conversations, chat, activity feeds and… well, you get the picture. Really, this seems like Facebook with an alternative color scheme and a different target audience.

But it does seem to be taking off — TechCrunch reported that the service was doubling its revenue every quarter, and it already successfully raised about $15 million in two rounds of fundraising. Yammer reportedly plays host to 80,000 companies — including 80 percent of the Fortune 500.

The competition has also failed to step up so far — despite the launch of Chatter, Salesforce.com’s take on Twitter for business, Yammer still continues to advance.

Yammer in its current form operates using the freemium model. It offers the basic service for free with a premium service charging $5 a month. The service crossed 1 million users in July. The company, based in San Francisco, launched in 2008, when it won an award at the TechCrunch50 conference, and is led by David Sacks, PayPal’s former chief operating officer.

The first set of applications will begin rolling out September 28. Until then, executives will probably just have to cross their fingers that employees won’t spend wasted hours on Yammer instead of Facebook. Or, worse yet, both Yammer and Facebook.