I visited a top floor of Goldman Sachs in the early 90s. They were using J, a dialect of APL. They still had those dumb little Bloomberg cube terminals on their desks, with the angry-fruit-salad colors scheme.

Nowadays it's in a window, but it looks the same. I don't know if they still use J, or K, but anyway not in real-time. That happens on FPGAs in a rack where traders once roamed.

But while APL cannot be said to be very popular, the most popular "time-series database" used in finance is published by APL fananics.