FSL is a collection of tools and software used to process fMRI, MRI and DWI data. Visit their installation page for download and installation guide.
FSL 6.0.2 and above are recommended. All testing has been done with FSL 6.0.2. PyDesigner has not been tested with other versions of FSL.
To check your FSL version:
$ flirt -versionA return value of at least FLIRT version 6.0 indicates successful installation of FSL, and that meets the PyD requirement.