LiteDB is serverless database delivered in a single DLL (less than 350kb) fully written in .NET C# managed code (compatible with .NET 3.5, 4.x, NETStandard 1.3 and 2.0). It is ideal for mobile apps or for small desktop/web apps, and its API is very similar to MongoDB C# Official Driver.
This code is linked to the post https://blog.georgekosmidis.net/2019/11/02/using-litedb-in-an-asp-net-core-api/