A+ a derivative of APL is still being used in a certain investment bank. 20 years of projects to deco it and replace it with something more modern haven't managed to completely kill it off yet. Main issue I had with it was the inability / cost to hire people with any experience, and the off-putting / steep learning curve. Once you get the hang of it though it's a great language for solving certain more numerically orientated problems.

Morgan Stanley. They open sourced it ~15 years ago at aplusdev.org. The project was led by Arthur Whitney, who went on to become Mr KDB.

Mr. Moneybags...well earned from what I hear.

Would you be able to comment about how much of it is the underlying APL (and math coded therein), and how much of it is the Electric GUI ?