fitsTcl is a binary extension to Tcl, providing simple access to astronomical data stored in FITS file format. fitsTcl implements a Tcl interface to the CFITSIO library, developed by the HEASARC (High Energy Astrophysics Science Archive Research Center) at the NASA Goddard Space Flight Center. fitsTcl is primarily distributed as part of the fv FITS file editor. It is also available by itself ; it requires CFITSIO which is a separate download. The license for both is GPL.