2 come to mind.
While consulting in college, I was contracted by Lexico for reference.com to write a wikipedia markup translator. The budget was small but it was one of my first big contract gigs. In the course of a loooong week, I put together a regular expression based PHP script with a small recursive descent parser for a couple edge cases. Of course this was before anyone really wrote unit tests, etc. I believe Reference.com used that for 10 years with only minor changes to support new syntax.
A few years ago, my neighbor received a 3M innovation grant in partnership with the Minneapolis Institute of Arts. He recruited an electrical engineer, a material scientist, and me (computer scientist). Between all of us, we developed a handheld device with a neo-pixel compass head that would navigate you through the museum and lead you to artwork you like. This involved using wifi triangulation and building a node map of every room in the museum. My key involvement was building recommendation system, which was a standalone cloud microservice that took in preference data (thumbs up/down buttons on the device) and using association rule mining to tell the hardware service which piece of artwork to lead you to next. I loved this project because I utilized more of my Computer Science degree. I also loved interfacing with hardware. This was pre IOT boom and it seemed all like magic getting custom built hardware to talk with cloud systems I put together. We also submitted the project to a scientific journal. At the time, it was such a departure from the dev lead role at a SaaS company and I really really enjoyed it.