Here are PGroonga users.
Zulip is a powerful open source group chat. It uses PGroonga to implement all languages support full text search. Because PostgreSQL built-in full text search feature supports only one language at the same time. PGroonga can support all languages at the same time.
(Send us your service description, how do you use PGroonga and why did you choose PGroonga.)
You can send your use case from https://github.com/pgroonga/pgroonga.github.io/edit/master/users/index.md .