Solo build. Ferguson's HR team was hand-transferring PTO data out of their iSolved HR system into WorkMax time tracking, every day, by hand. I replaced that with a Python ETL pipeline: pull the PTO data from iSolved, transform it, load it into WorkMax, once a day on a GitHub Actions cron. It saved the HR staff over an hour a day each.
The wrinkle was that this was the first API WorkMax had ever shipped, so building against it meant being its first real consumer and finding the rough edges of a brand-new integration surface as I went.