I’m seb and i bootstrapped cloudXLS.com into private beta beginning of this year. The idea for that tool I had around 3 years ago, when we replaced a full rails app with a daily updated 15mbyte excel report. Huge win for us (got rid of a legacy system) and for the client (all the metrics he needs available instantly and transparently).
This was quite a turning point - before Excel was always my enemy (no Unicode support for CSV, html-tables-as-xls slow to load, ugly, poor on features, etc) but after that project I saw the potential when fully embracing that tool.
So, sometime last year I decided to get real and started working on some prototypes in between (Ruby/Rails/JS) consulting projects. After some pivots, I decided my first version to be an API that basically merges your CSV data into your xls files that contain the formatting, charts and formulas.
So I launched into private beta in January, feature freeze, and focussed on copy, marketing pages, which is kinda challenging for a coder. First customers in, and already pumping out excel files. Now i’m getting ready to open up the private beta.