Mantle is the API AMD unveiled last year alongside their AMD Radeon R9 290 "Hawaii" graphics cards. While it was billed as a high-performance graphics API, in its current form it turns out that it's more of a benefit to low-end CPUs that are bottle-necked rather than an interface that can better speed along high-end GPUs in all situations.
With this Mantle Windows driver it turns out that all "GCN" GPUs are not supportd but only the Radeon R9 290X, R9 290, R7 260X, and AMD Kaveri APUs.
Since Mantle's announcement in October we have wondered about Mantle Linux support. AMD later said they want Mantle on Linux and other platforms but with today's long awaited release, there is no indication of Linux support (or non-Windows platforms) support coming anytime soon. Hopefully some of the lessons learned from Mantle can just be folded back into future revisions of OpenGL to render this graphics API unnecessary.
Judging by the limited Windows games offering up a Mantle renderer at this time, the very limited hardware support, and the performance wins being mostly for lower-end CPUs, Linux users fortunately don't seem to be missing out. The updated Windows software for Mantle is available from AMD.com.