It's funny how sometimes you use a tool for years, but still find out new functionality once in a while.
But sometimes ... there is no escaping those though debugging sessions.
I work in embedded software, so debugging tends to be done with plain old gdb+gdbserver.
I would like to use QtCreator's remote debugging features, but they require gdb/gdbserver to be compiled with python support.
And guess what? I don't have that at the moment.
TUI stands for Text User Interface, and is a sort of ncurses UI built right into vanilla gdb.
You access it by pressing C-x A. And voila : you can now debug while seeing the code you are stepping through.