In the 1990s Morgan Stanley's full suite of fixed income portfolio management and trading applications were written in APlus which was another of Arthur Whitney

In the 1990s Morgan Stanley's full suite of fixed income portfolio management and trading applications were written in APlus which was another of Arthur Whitney's APL variants. When I joined, MS was moving away from it, but the developers who'd been using it were very much in the "you'll take APlus from my cold, dead fingers" camp.