I built a search engine for sales taxes in Canada. Just type in a product or service and it would tell you whether it was taxed, and what that tax was (HST, PST, GST, zero-rated etc). It was a huge endeavour. I had an investor. I hired a half dozen data-entry people to input items. I personally went up and down the aisles of Walmart documenting every item on the shelves. I used Amazon.com product hierarchy to categorize the entries.

I worked night and day for three and a half months. I would literally collapse on the floor with exhaustion and be unable to move.

When I think about it now I marvel at the gargantuan scope of the project and my unrelenting drive to finish it. It was probably the most ambitious undertaking of my life.

And when it was finished - 12,000 easily searchable items and their sales tax for each of the 10 provinces and three territories - NO ONE CARED. People on reddit mocked the idea. I pitched it to an incubator and they shrugged indifferently. A few months later I repaid the investor (I didn't want him losing money because of my shortsightedness). Eventually the site was taken down, although I wish now I didn't.

It's here on archive.org, if you're interested, although it doesn't show the output: https://web.archive.org/web/20180118173228/http://www.isitta...