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Ed Wible is a founder of Nubank and chose Datomic. He and Lucas Cavalcanti gave a talk on it at Clojure/conj 2014.

Ed's post when Cognitect joined Nubank is still a great read: https://building.nubank.com.br/welcoming-cognitect-nubank/

There are some videos, both of the start and of their progress. Some of the most impressive work I have ever seen, remarkable.