SQLite as Application File Format
→ https://www.sqlite.org/appfileformat.html
The SQLite docs have a fantastic page about why SQLite works as an application file format. The arguments are convincing: ACID transactions, extensible without format migrations, performant on partial reads, and universally toolable.
Anyone who has ever built their own binary format or nested JSON as a storage format knows the pain. SQLite solves this elegantly.