FAUST is a functional programming language for realtime audio digital signal processing. The Faust compiler can generate code in lower-level programming languages such as C, C++, JAVA, LLVM bitcode, WebAssembly, etc. Code generated by the FAUST compiler can be turned into a wide range of objects (e.g., audio plug-ins, smartphone apps, web apps, etc.) for various platforms (e.g., Linux, Windows, MacOS, etc.). By also allowing us to target embedded systems such as microcontrollers, DSPs, FPGAs, embedded Linux systems, etc. and by providing a set of tools to implement physical models of musical instruments, FAUST is particularly well suited to design hybrid acoustical and digital musical instruments mixing physical and virtual elements. After giving an overview of the aforementioned tools, we demonstrate how they can be used for designing novel hybrid instruments.