As promised when AMD revealed their answer to NVIDIA's DLSS, FidelityFX Super Resolution (FSR) is now officially open source and available under the MIT license.
What actually is it? AMD say "FSR uses super-optimized spatial upscaling technologies to help boost your framerates and deliver high-quality, high-resolution gaming experiences, without having to upgrade to a new graphics card.". It works on both AMD and NVIDIA GPUs too, so it's not locked to a vendor. The idea is to give "practical performance" for more costly rendering operations like Ray Tracing.
This open sourcing was announced today, along with information on both Unity and Unreal Engine will be supporting it for many more game developers to use. For Unity it's available in a special Unity 2021.2 HDRP release, while AMD provide special Unreal Engine patches for developers to add into UE to support it.
It already works just fine on Linux, and you can see it with the native title Dota 2 which already has it hooked up. You need to use Vulkan though, as AMD don't support it with OpenGL. FSR will work with both native Linux titles and Steam Play Proton too.