Here is the entry point for resources related to work with APL and J. Developed over the years, this material has ended up in out-of-print manuals, old APL systems, archives, personal computers, and hidden corners of the Internet.
Here it is freely available on the Internet in a more modern format.
A large freeware collection of utility functions written in ISO APL ("standard" APL)
Comprehensive list of annotated links related to APL.
Miscellaneous Topics in APL and J
Various papers, notes, essays, software etc. on APL and J programming languages