Both technologies synchronize the refresh rate of your video card with your display, resulting in smoother gameplay by eliminating stutter and tearing issues. AMD's FreeSync is a software-based solution that uses the royalty-free DisplayPort Adaptive-Sync industry standard, while NVIDIA's G-Sync is a hardware-based solution.
As PC World reports, the big problem right now is that there's no cross-compatibility. In theory, NVIDIA could adopt FreeSync, but the company prefers to keep pushing its G-Sync technology.
There’s a nasty anti-consumer downside to this display technology war between AMD and Nvidia: The lack of cross-compatibility. The benefits of FreeSync displays only work with Radeon graphics cards while G-Sync’s charms are restricted to GeForce cards. With many gamers buying monitors far less frequently than graphics cards, the threat of brand lock-in is real. Here’s hoping AMD and Nvidia cast aside their difference to rally around a single standard at some point in the future—but don’t hold your breath.