APL had non trivial uptake during its heyday. J is apparently somewhat popular with actuaries and similar. K/Q is used by a number of finance companies, via t

APL had non trivial uptake during its heyday. J is apparently somewhat popular with actuaries and similar. K/Q is used by a number of finance companies, via the KDB vector database. Here the selling point was that the overall system was great for in memory vector processing of stock tick data. Arthur Witney also built a language named A+ while at Morgan Stanley that was used in production as an improvement over various previous APL apps. They're odd languages but have found successful niches.