CSV Explorer, 4 months ago (https://news.ycombinator.com/item?id=14043527). It's a tool to open CSVs that are too big for Excel. It hit the homepage, but many comments were "I would never trust my data in the cloud" or "Why doesn't everyone use Python/Pandas/SQL".
Paying customers now include consultants, journalists, realtors, insurance companies, and others! There are few developers who use it because it saves them time, but they're the exception.