AMD today officially announced FreeSync, an open-standard technology that makes video and games look more fluid on PC monitors, with fluctuating frame-rates. A logical next-step to V-Sync, and analogous in function to NVIDIA's proprietary G-SYNC technology, FreeSync is a dynamic display refresh-rate technology that lets monitors sync their refresh-rate to the frame-rate the GPU is able to put out, resulting in a fluid display output.
FreeSync is an evolution of V-Sync, a feature that syncs the frame-rate of the GPU to the display's refresh-rate, to prevent "frame tearing," when the frame-rate is higher than refresh-rate; but it is known to cause input-lag and stutter when the GPU is not able to keep up with refresh-rate. FreeSync works on both ends of the cable, keeping refresh-rate and frame-rates in sync, to fight both page-tearing and input-lag.
What makes FreeSync different from NVIDIA G-SYNC is that it's a specialization of a VESA-standard feature by AMD, which is slated to be a part of the DisplayPort feature-set, and advanced by DisplayPort 1.2a standard, featured currently only on AMD Radeon GPUs, and Intel's upcoming "Broadwell" integrated graphics. Unlike G-SYNC, FreeSync does not require any proprietary hardware, and comes with no licensing fees. When monitor manufacturers support DP 1.2a, they don't get to pay a dime to AMD. There's no special hardware involved in supporting FreeSync, either, just support for the open-standard and royalty-free DP 1.2a.
AMD announced that no less than 12 monitors from major display manufacturers are already announced or being announced shortly, with support for FreeSync. A typical 27-inch display with TN-film panel, 40-144 Hz refresh-rate range, and WQHD (2560 x 1440 pixels) resolution, such as the Acer XG270HU, should cost US $499. You also have Ultra-Wide 2K (2560 x 1080 pixels) 34-inch and 29-inch monitors, such as the LG xUM67 series, start at $599. These displays offer refresh-rates of up to 75 Hz. Samsung is leading the 4K Ultra HD pack for FreeSync, with the UE590 series 24-inch and 28-inch, and UE850 series 24-inch, 28-inch, and 32-inch Ultra HD (3840 x 2160 pixels) monitors, offering refresh-rates of up to 60 Hz. ViewSonic is offering a full-HD (1920 x 1080 pixels) 27-incher, the VX2701mh, with refresh-rates of up to 144 Hz. On the GPU-end, FreeSync is currently supported on Radeon R9 290 series (R9 290, R9 290X, R9 295X2), R9 285, R7 260X, R7 260, and AMD "Kaveri" APUs. Intel's Core M processors should, in theory, support FreeSync, as its integrated graphics supports DisplayPort 1.2a.
On the performance side of things, AMD claims that FreeSync has lesser performance penalty compared to NVIDIA G-SYNC, and has more performance consistency. The company put out a few of its own benchmarks to make that claim.
For AMD GPUs, the company will add support for FreeSync with the upcoming Catalyst 15.3 drivers.