FreeSync over HDMI was showcased as a concept at this past June's Computex in Taipei, but now it's very real and very official.
As you may know, HDMI doesn't support AMD's smooth gameplay tech by default -- a DisplayPort-equipped monitor is required. However, it can support it via the introduction of "specific, proprietary extensions that introduce the necessary variable frame-rate technology", and this is exactly what AMD is doing. They're not offering further details on the extensions at this stage, but the important thing is you don't have to shell out for a more expensive DisplayPort monitor to experience the tech.
Any video card that supports HDMI 1.2 or later will, in turn, support FreeSync over HDMI, once combined with an upcoming driver. Then all you need is an appropriate scaler/monitor, which it's possible you already have. Samsung is the only confirmed manufacturer to have monitors out that support it as of yet, but there may be others. If you're interested enough, check with your manufacturer to see if your display includes the necessary scaler. Starting in 2016, some new, some refreshed monitors from LG, Acer, and Samsung will be marketed as supporting FreeSync over HDMI.