This is a PHP wrapper for FFTW library.
The extension can be installed on Linux.
First download the source
git clone https://github.com/bukka/php-fftw.git
Then go to the created source directory and compile the extension. You need to have a php development package installed (command phpize must be available).
cd php-fftw
phpize
./configure
make
sudo make install
Finally you need to add
extension=fftw.so
to the php.ini