A while ago I built Calendar Butler. In my free time, for people who work for several clients at once. It runs, it has users, and it saves them a lot of time every year.
Recently I was in conversation with a company that would like to use Calendar Butler. They had recognized the benefit and calculated that the tool would save them about 3 full-time positions that are really only busy with pointless work, and that those people could do meaningful things instead.
Then my contact said something that floored me: “I see two options. The first: we somehow get it running on our own servers. The second: we just build it ourselves.”
To them it was a 'small tool someone wrote on the side'. That it is a product, with a customer base and on a path of expansion, had not occurred to them at all.
