HM Revenue & Customs`, the UK's tax body, has transformed its services using microservices architecture built on `MongoDB`'s scalability, data model flexibility, and ease of development. The transformation led to a significant reduction in wait times for self-assessment returns, with wait times cut in half to around 5 minutes. This improvement resulted in an unprecedented number of online submissions, with 89% of customers using the new system, saving £8.2m in operational costs and receiving increased efficiency through agile development and open-source technology adoption.