Send to Dropbox. Allows you to email attachments to your Dropbox. Makes roughly $2,500 a month currently. More info in this other thread: https://news.ycombinator.com/item?id=8699687
I wrote my app before Dropbox had published any branding guidelines for developers (3+ years ago), so I was essentially grandfathered in. Perhaps my phrasing of "special exemption" was a bit strong. I apologize for that. I dug up this email exchange: http://i.ralph.io/95cc7ww3.png
They're essentially paying for the ability to customize their email address, set up incoming whitelists/blacklists (so someone with your address can't fill up your Dropbox overnight), as well as expedited email support.
I created sendtodropbox.com (email attachments to Dropbox) as a side project about 3 years ago. After the initial prototype, two-ish rewrites, and monetizing it with a freemium model, it's now got 1100 paying subscribers and brought in $20k in revenue this year. I did the whole thing myself (aside from the website template design, which a buddy of mine helped out with). This doesn't technically fall under the "informative value" category, but going solo on a project to make it profitable is definitely possible.
Node.js + React -- we're going to upend the finance industry.
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