Final answer:
Bill Gates and Paul Allen wrote: Microsoft BASIC, an early programming language for personal computers.
Step-by-step explanation:
Bill Gates and Paul Allen, at the ages of 19 and 23 respectively, wrote Microsoft BASIC. This programming language was instrumental in the early development of personal computers. It allowed users to write and run programs on Microsoft's early operating systems.
Bill Gates and Paul Allen wrote Microsoft BASIC, which was a fundamental programming language for early personal computers. This contribution aided the rise of Microsoft in the rapidly growing personal computing industry during the late 1970s and early 1980s, a time when Apple also established itself with the introduction of user-friendly interfaces.