- Small resource requirements. RetroBSD requires only 128 kbytes of RAM to be up and running user applications.
- Memory protection. Kernel memory is fully protected from user application using hardware mechanisms.
- Open functionality. Usually, user application is fixed in Flash memory – but in case of RetroBSD, any number of applications could be placed into SD card, and run as required.
- Real multitasking. Standard POSIX API is implemented (fork, exec, wait4 etc).
- Development system on-board. It is possible to have C compiler in the system, and to recompile the user application (or the whole operating system) when needed.
Via the comments.