When I joined Privalia, they were having a hard time maintaining their product. There were 4 different front-end platforms (very similar between them) for 4 different countries. Bugs and problems were popping up every day due to outdated components and the duplicated code bases.
Even with the delays of the project, I think this was one of the more successful projects I have been a part of. Giving birth to an integrated multilanguage platform for 4 different countries and serving more than 4 million users at that time is something I was lucky to experience. I also feel proud of doubling the conversion rate of the last steps of the checkout process through multiple redesigns and A/B testing. Overall, we managed to decrease maintenance and bandwidth costs, as well as time to market for new features.