There’s a lot of software around for modeling UML, but much of it is old and has halted development or is part of an IDE.
When you are working with version control system, you tend to do the same operations over and over all the time. Therefore you should take every shortcut you can find to make the process as smooth as possible, limiting the amount of text you type.
I’ve recently stumbled upon a new cli program called tmux. This program is similar to the old program screen which can be found in many nix systems.