DuckDb supports reading/writing to a SQLite database, while using the improved DuckDB syntax. Sounds too good to be true, but I keep meaning to explore if there are any obvious gotchas.
Other than that it's awesome. I've stuck to its native file format though as scanning SQLite is slower.
Perform OLTP actions against sqlite db from within duckdb.
Perform OLAP actions against duckdb db from within duckdb.
Sometimes your OLTP content drives the OLAP query so read from both sqlite db and duckdb db at the same time.