Evolu (a local-first platform designed for privacy, ease of use, and no vendor lock-in) has been using Effect for many months, and I'm close to releasing a refactoring that will embrace Effect even more (some modules didn't exist when Evolu switched from fp-ts to the Effect).

Effect is a great library, but it has one probably unresolvable issue. Once you use it, you will never want to write TypeScript code without it.