BoltDB is a key/value local storage with simple API but powerful transactions and ACID support.
Main goal of the project is to provide a simple, fast, and reliable database for projects that don’t require a full database server such as Postgres or MySQL. It is used in high-load production with database sizes up to 1Tb.
1Tb is not that much actually, but since its main competitors are RocksDB/LevelDB and LMDB it is quite spectacular volume. Main differences between BoltDB and RocksDB/LevelDB are on-disk structure and transaction support – RocksDB and LevelDB are designed on top of LSM trees and thus are well-suited for write load, while BoltDB uses B+-tree – this generally scales better for read workload. LevelDB doesn’t support transactions, while BoltDB does (and it uses very nice and convenient API).
Main difference between BoltDB and relation databases like Postgres or MySQL is, well, relation – BoltDB is a simple key/value store (although its API supports cursors, transactions, prefix key search).
Worth considering for local storage: https://github.com/boltdb/bolt