Maybe this doesn't count because I wasn't really serious about making money with it. Long time ago, I wrote an unofficial iPhone app that you could use to log into your Vonage account and listen to your voicemails, rather than using their (then) not-mobile-friendly web site. Vonage did not publish an API, so I scraped their online portal's HTML and figured out what GET calls were needed, and just mimicked them from the app.
Of course it was totally vulnerable to 1. Vonage deciding to change their backend or internal API and 2. Vonage deciding to legally destroy it, neither of which happened. At the end of the day I didn't put any marketing into it and decided it was too niche to continue supporting so dropped it from the app store. Took a few months of weekend work to do the first release and then a couple of days a month to maintain it.
Of course it was totally vulnerable to 1. Vonage deciding to change their backend or internal API and 2. Vonage deciding to legally destroy it, neither of which happened. At the end of the day I didn't put any marketing into it and decided it was too niche to continue supporting so dropped it from the app store. Took a few months of weekend work to do the first release and then a couple of days a month to maintain it.