What host O/S have you used? List experience from most to least used.

Host operating systems are the development-machine OSes used to write, build, and debug embedded software (as distinct from the target's firmware/RTOS). The common host OSes are:

• Linux — widely used for embedded toolchains, cross-compilers, build systems, and command-line development; common for kernel/driver and BSP work.
• Windows — common for vendor IDEs, debuggers, and many commercial embedded toolchains.
• macOS — Unix-based, used for development with GCC/Clang toolchains and cross-development.

Each can host cross-compilers, debuggers (JTAG/SWD via tools like OpenOCD/GDB), version control, and emulators/simulators for the target.