I got some old applications which is using spring.net and nhibernation with sqlite. By these names, you can know those frameworks are very old. That is the time to modernize them. I have research some local database solution. You can use System.data.sqlite, that is very light weight, but that is a plain sql without ORM. Or you can use MSSQLLocalDB with entity framework. But the SQL Express is still required. Finally, I found liteDB. This is a local NoSQL framework. You can add a single DLL into your project, not even simpler, just use Nuget to install it. The code syntax is similar with MongoDB.
Moreover, it has GUI tool LiteDB Studio, you can query the db file. Lastly, I checked the latest git commit is only 4 hours only. The project keeps to be active