APEX APL compiler from Snake Island Research
APL+Win Tools for Programmers: Rex Swain has contributed many tools for APL developers at APL2000 User Conferences. PDF file ucmdsrex.pdf shows the tools; user-command file ucmdsrex.sf contains the code.
Array Editor supports editing arbitrary arrays. http://www.davidliebtag.com
Dyalog APL/W auxiliary processors for access to APL*PLUS/PC data structures from <jgoff AT VERY SPAMMMFRE beautifulsystems DOT com>
Inca software change management system from HMW <hmw AT VERY SPAMMMFRE 4xtra DOT com>
Maya APL code file manager from HMW <hmw VERRYY SPAMFRE AT 4xtra DOT com>
Olmec APL GUI environment from HMW <hmw SPAMMFREE REALLY AT 4xtra DOT com>