Using it as a cache for exported functions, structs, etc in already compiled files in my incremental compiler project for the language I am designing. The first time you compile a file its exported entities are added to the table, then if you don’t change the file you can skip compilation of said file.
Working well so far but I feel like it’s a little much for the job.
I use it for a personal notes app, any Android app I have made. I don't think I have needed a serious DB like postgres for any project in the last 5 years, sqlite has been more than enough.
If I were at the same scale as Facebook or Google I would probably pick something with a better concurrency story though.
I use it as the storage engine for rqlite, a distributed relational database.