Sales taxes are confusing in Canada, because many products and services are taxed according to where you live in the country. I thought that was a problem Canadians would like solved.
In reality, most people just assume everything but food at the grocery store is HST taxable. They think they know the tax rates and will not challenge their own assumptions.
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.