SQLite has been used on top of a lot of things, including FoundationDB (https://apple.github.io/foundationdb/architecture.html https://apple.github.io/foundatio

SQLite has been used on top of a lot of things, including FoundationDB (https://apple.github.io/foundationdb/architecture.html https://apple.github.io/foundationdb/architecture.html). That's different than using the DB directly though.