There have, historically, been two kinds of operating systems: general-purpose, and special-purpose. These roles are defined by the function they serve for the user. Examples of general-purpose operating systems include Unix (Linux, BSD, etc), Solaris, Haiku, Plan 9, and so on. These are well-suited to general computing tasks, and are optimized to solve the most problems possible, perhaps at the expense of those in some niche domains. Special-purpose operating systems serve those niche domains, and are less suitable for general computing. Examples of these include FreeRTOS, Rockbox, Genode, and so on.