I have a B2B lead generation and marketing SaaS for the UK market. It's used mostly by accountancy firms and insurance brokers, but also by people in HR, venture capitalists, enterprise salespeople, and more. It gives you the ability to search and filter through the millions of records in Companies House and it's updated every day. It's all written in Haskell, and it's been running for a few years now.

https://newbusinessmonitor.co.uk/