"Facebook at Work" smartphone applications appear in Apple's online app store and the Google Play shop for Android-powered mobile devices, but can only be accessed by a few companies collaborating with the social network.
The pilot program is intended to gain feedback to refine the offering, according to Facebook spokeswoman Elisabeth Diana.
"We have internally used Facebook at Work for many years now, it works pretty effectively and efficiently for collaboration," Diana told AFP.
"We think we can bring this insight to other companies."
Facebook at Work has news feeds, chats, groups and other features that can be found on the widely-used social network, but sharing can only be done with people inside a particular company.
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Page backgrounds are a different color from the well-known Facebook blue, ostensibly so bosses will know at a glance when social networking is work-oriented.
The customized work social networks are hosted on Facebook servers in the Internet cloud, but each respective firm controls any data shared by its employees.
Diana would not disclose what companies are involved in the pilot program, but did say some had offices in various countries.
California-based Facebook did not discuss how it will make money from workplace versions of the social network, but it could follow an established model of charging subscriptions to it as a cloud-based service.