High Quality Content by WIKIPEDIA articles! The GNU Data Language (GDL) is a free, compatible alternative to IDL (Interactive Data Language).. Version 0.9.1, released in March 2011, has full syntax compatibility with IDL 7.1 and supports some IDL 8.0 language elements as well. GDL is in beta stage of development. Together with its library routines GDL is used as a tool for data analysis and visualization in such disciplines as astronomy, geosciences and medical imaging. GDL is licensed under the GPL. Other open-source numerical data analysis tools similar to GDL include GNU Octave, NCL - NCAR Command Language, PDL - Perl Data Language, R, Scilab, SciPy, Yorick.