Other forms of software design: user interface design, framework design, database schema design, communication protocol design, or mobile application design, …
Tailoring Principle languages for specific domains: for the design of control systems, enterprise applications, games, multimedia systems, aerospace applications, software for the the automotive industry, …
Principle languages for certain non-functional requirements: performance, reliability, security, …
Principle languages for other levels of abstraction: architecture, requirements analysis, algorithm design, coding, …
Principle languages for other programming paradigms: procedural programming (C, Pascal, …), functional programming (LISP, Haskell, …), fourth generation programming languages (Progress, ABAP, …), scripting languages (bash, ruby, python, PHP, …)