FLATlib is a simple, lightweight Fortran90 library for convolving a theoretical source with the Fermi-LAT IRFs (energy dispersion, point-spread function and effective area). Its source is freely available for download.
The current FLATlib beta is presently only minimally documented, but this is anticipated (hoped!) to change soon.
From v0.7 onwards, you can get FLATlib from the
FLATlib public GitHub repository
Previous versions can be downloaded here: