I develop CoCoA (an open source computer algebra system in C++) with a textual interface. We also have a Qt interface, but it is too hard for us to develop and maintain it.

Personally I use Emacs: I defined the syntax for our programming language, and how to send commands from a text file to another window with the textual program running.

It would be nice to have such an "empty interface" in Qt allowing basic editing and running a process, but I cannot find one.