J Systems are available for Windows 9x/NT/2000/CE, Macintosh, Linux, Solaris, AIX, FreeBSD, NetBSD, and others. The core language is identical in all versions, and programs not making use of platform-dependent features will work unchanged on all systems.
J is free on all platforms! You can download, redistribute, and run J for free. There is a fee for a professional key (prokey) that enables features required for commercial development of large systems.
A prokey enables: debug suspension, performance monitor, and ijl encoding. The prokey is set in the Edit|Configure|License (query/set 9!:30 and 9!:31). 13!:0[1 (debug suspension) or 6!:10 (performance monitor) or 3!:6 (ijl encode) fail with domain error if a prokey is not set.
A prokey is licensed for a single J system. You must not use the same prokey on different systems.
J is documented in the J Dictionary, J Phrasebook and J Primer. The full texts of these manuals are also included in the on-line help.
You can download these systems from www.jsoftware.com.