Programmers, like carpenters, are builders — we make things. The work can be for pay, but carpenters, for example, can build their own bookshelves and doghouses. Programmers also make software for themselves, sometimes to amuse, sometimes to provide a useful function.
A few of the apps I created for myself over the years turned out to be major workhorses for me — tools I used frequently. One of the earliest was PF.EXE, my Process File utility.