The Mailbox Multitasker is portable multitasking environment written in ``C''. The package, which may be uploaded from BIX, serves both as an educational illustration of how a multitasker can be can be built, and as a productivity tool which you may incorporate in your own programs and modify to suit your needs. With the Mailbox Multitasker you may write multitasking programs which are portable to many different machines and operating systems. What is more, should the machine have multiple processors, your program can take advantage of them and may run significantly faster.