The following interpreters are, with one exception, available by download. Terms and conditions vary. Some vendors offer free versions for educational or non-commercial use.
A+ is an APL descendant originally developed for financial-markets applications at Morgan Stanley, an investment bank, now released as open-source. The BAA distributes a free implementation for Windows. Uses only ASCII characters.
APLX is a cross-platform APL with native support for charting, image manipulation, database, networking, email and HTTP objects. Evaluation-period versions are available free for Windows and MacOS, and a personal-use version is free for Linux users.
APL2 is a well-established interpreter from IBM for mainframes and Windows. It can be downloaded free by FTP for DOS or Windows. Both versions have limitations – see the readme.txt files or the APL2 page for details. Educational licences are available.
APL2000 interpreters (APL+Win, APL+Unix and APL+Linux) are closely integrated with their respective development environments. Enterprise, developer, classroom and downloadable evaluation versions are available. Ajay Askoolum is an experienced Windows developer; his cookbook System Building with APL+Win (2006) was reviewed in Vector and is available from Amazon.
Dyalog is a full-featured APL development environment for Windows and PocketPC, with support for .Net and OO, and runtime versions for Linux, MacOS and Unix. Educational and non-commercial licences are available. The current version has full, native support for Unicode. Bernard Legrand’s textbook Mastering Dyalog APL (2009) is available from Amazon or as a free PDF download from the book’s website.
GNU APL is a free interpreter for the programming language APL. The APL interpreter is an (almost) complete implementation of ISO standard 13751 aka. Programming Language APL, Extended.
I-APL is an ISO-compliant APL for DOS available free from the BAA. Largely of historical interest now, there are versions for the following micros:
J is Iverson’s rebuild of APL from scratch, revising earlier design decisions in the light of experience, and incorporating insights and abstractions of considerable power. J is particularly valued for mathematical work, runs on Windows, Unix, MacOS and PocketPC, is free for non-commercial use and ships with extensive tutorials. Howard Peelle’s textbook Mathematical Computing in J (2004) was reviewed in Vector and is available from Amazon.
q wraps the K language and the kdb+ database, and is much used in financial markets for fast handling of very large datasets. While commercial licences are beyond the reach of most individuals, Kx Systems offers a free version of the language, and q programmers are in demand. There are interpreters for 32-bit and 64-bit Solaris, Linux and Windows machines. Uses only ASCII characters. Jeffry Borror’s textbook q for Mortals (2008) was reviewed in Vector and is available from Amazon.com.
NARS2000 is an ISO Extended APL compliant interpreter available as free open source software for Windows platforms and any other platform capable of running Wine (which means almost all Linux systems).