Any of you paranoid people who answer #asknostr questions able to recommend an mqtt app?

Mqtt seems great on homeassistant and on Arduino but I need a way to get between them for testing and development. All those applications seem loaded with SaaS BS like cloud accounts and subscriptions that serve no use other than spying and revenue extraction. This is for traffic that never leaves my private home network subnet, why are features locked behind a cloud account and subscription?