The NAS FFTW library is an optimised implementation of the well-known FFTW library (see http://www.fftw.org for details). The following implementations are available.

PowerPC 74xx with G4 vector processor running under Linux or VXWorks 5, single-threaded.
MIPS64 running under Linux, threaded for multicore processors.
For licensing reasons these libraries are available from:
DRS Signal Solutions Inc.
700 Quince Orchard Road
Gaithersburg, MD 20878, USA
Tel: +1 301 948 7550
Intel with SSE2 under Linux, threaded for multicore processors. Major speed advantages are provided relative to the Intel MKL library (where comparable routines exist) and to the open source versions of FFTW.
This library is (as of January 2008) at beta release.

Further information is in the following documents:

Datasheet:Optimised FFTW Libraries
Datasheet:Optimised FFTW Libraries - Outline Documentation