The NVIDIA Vulkan Linux driver.. As said in the article, goes back to the Kepler era - https://developer.nvidia.com/vulkan-driver.
The Radeon Windows Vulkan driver... No Linux driver today, see my article for more details - support.amd.com.
Intel - no download link yet for the user-space component. More details coming.
All of the open-source goodies are via KhronosGroup on GitHub.