GNU APL

GNU APL is a free and (almost) complete implementation of Extended APL as specified in ISO/IEC 13751:2001 and is thus similar to APL2. It was initially written and is being maintained by Jürgen Sauermann. It includes extensions such as complex numbers and a shared variable interface.

In addition to a normal local APL session, GNU APL can be scripted, and has an experimental online version.

Documents on GNU APL sometimes quote Richard Stallman, who both founded GNU and programmed in APL. However, Stallman is not directly associated with the project.

Encoding
GNU APL tends to prefer the Unicode Lozenge (U+25CA; ) and Element of (U+2208;  ) over Diamond operator (U+22C4;  ) and Small Element of (U+220A;  ) which are more commonly used by other dialects. This can lead to SYNTAX ERRORs if attempting to use code written for GNU APL in other implementations. However, GNU APL also accepts the more common code points.