Facebook is testing a free version of workplace as it aims to expand the service and get more people on board with using it as their main tool for workplace communication and collaboration. Workplace in its free status has become Workplace Standard, so as to differentiate the no-cost offering from the paid version of the tool that is already available to any business that wants to use it, now called Workplace Premium. Facebook's goals for Workplace Standard are more than just expanding its userbase for the software though.
According to Facebook they want Workplace to be more accessible in emerging markets and they understand that not every company or business may be able to pay for the cost of the Workplace Premium service, which starts at $3 per user for the first 1,000 active users and goes down from there. Facebook cites that India is the top market for Workplace currently and it wants more emerging markets to have access and potentially grow just as big of a userbase. It also sees Workplace Standard as a way to get people interested in trying the service out so they get their foot in the door to see if they like the tool. If they do, Facebook is hoping that those who are using the free tier of Workplace will opt to step things up to the premium option.
For the most part Workplace Standard and Workplace Premium seem to offer mostly the same experience. There doesn't seem to be a limit to how many users from an account can access to the tool for collaboration purposes, or Facebook simply doesn't mention it. There are some differences though that could be an incentive for people to move from Standard to Premium as the Premium tier software has analytics tools as well as controls for administrators, which makes the software that much more of a safe piece of software as admins will be able to set limits on various elements. As this is only in testing right now it wasn't made clear how long Facebook plans to test it out before making it more widely available, and where they plan to launch it first if it doesn't launch globally from the beginning.