Read this: Apple released the Macintosh Plus on January 10, 1986, for a price of US$2,600. It offered one megabyte of RAM, easily expandable to four megabytes by the use of socketed RAM boards. It also featured a SCSI parallel interface, allowing up to seven peripherals—such as hard drives and scanners—to be attached to the machine. Its floppy drive was increased to an 800 kB capacity. The Mac Plus was an immediate success and remained in production, unchanged, until October 15, 1990; on sale for just over four years and ten months, it was the longest-lived Macintosh in Apple's history. In September 1986, Apple introduced the Macintosh Programmer's Workshop, or MPW, an application that allowed software developers to create software for Macintosh on Macintosh, rather than cross compiling from a Lisa. In August 1987, Apple unveiled HyperCard and MultiFinder, which added cooperative multitasking to the Macintosh. Apple began bundling both with every Macintosh.

In 1984, what did Apple introduce to allow developers to create software for Macintosh on Macintosh?
What is the answer? (If it cannot be answered, return "unanswerable")
unanswerable