I can't seem to find it but I think unsplash was a similar side project that was used as marketing for a different company.
Unsplash [1] was a side-project for our company freelance developer and designer platform, Crew [2] (Crew was later sold to Dribbble; Unsplash now operates independently).
We knew as creators that finding beautiful, useable imagery was one of the hardest challenges in any creative project, so we decided after shooting some photos for our homepage header image, to give the rest of the photos from the shoot away for free for anyone to use.
We setup a $19 tumblr theme, a domain, and posted the site to here.
What happened next was amazing: the site was flooded with traffic thanks to trending on HN, thousands of photos were downloaded on the first day, and most shockingly to us, other creatives began submitting their own photography to Unsplash.
Fast forward a year later and Unsplash was the main source of traffic and revenue for the parent company Crew. I think it peaked at around 60% of our monthly revenue due to customers finding Crew from a simple 'Made by Crew' link on Unsplash. At the same time, Unsplash was doing around 1M downloads a month.
We eventually sold Crew to Dribbble to focus full time on Unsplash, so it's no longer a side project. It's grown a lot since those early days, with more than 20M photo downloads every month, half a million free-to-use photos, and is integrated into thousands of applications, including Trello, Adobe, and more.
If you're interested in more about Unsplash, we've got all the main milestones here: https://unsplash.com/history
1 - https://unsplash.com 2 - https://crew.co
It got so successful that they split it into two companies at some point (I can't find the reference blog post talking about this right now, so if anyone does feel free to comment)