It was launched alongside money.js[1] (a minimal JavaScript currency conversion library), designed to work seamlessly together and both found a brilliant response and grew an organic community.
Hundreds of tutorials and thousands of posts and mentions later, GitHub eventually contacted me and politely asked me to take down the exchange rates repository, because they were being hammered by people requesting the data - only at this point did it occur to me that I'd created something of genuine value, and (6 months of fretting and tail-chasing later) I opened up a paid option.
For me the key thing was: I never intended to create a business. It was (and is) a labour of love. We've since grown to be the industry-leader for our area - "good enough data" for the startup and SME market - and count Etsy, KickStarter, WordPress and Lonely Planet among our clients.
Although it's no longer truly open source, 98% of our users are still on the Free plan, which will very soon be expanding to include all features (so, no more limiting by price tiers) - this is how I still feel so passionate about it.
I can't wait to publish the next steps in our journey - where we're opening everything up to the community and marketplace. I don't like where the industry is heading (competitive, closed, secretive) and we've chosen to move towards transparency and sharing.
I like businesses built on a core of open source community, because they're in service to the people who are actually building the products, rather than those in the traditional 'upper levels'. This means there's really no "sales process" (which I'm massively allergic to) - apart from the occasional grilling from the accounting department, who may find it hard to trust a business based on open source principles.
Good luck!