FFTW is available under two distinct licensing options:
1. Commercial License Options and Pricing
- FFTW 3.3.x ($12,500) Download License Here
- FFTW 3.2 ($7,500) Download License Here
- FFTW 3.1 ($7,500) Download License Here
- FFTW 2.1 ($2,500) Download License Here
2. Free Open Source License
- Open Source (GNU GPL v2 License) Download Here
You are free to redistribute it and/or modify it under the terms of the GNU General Public License version 2 as published by the Free Software Foundation.