a sample rank for dotnet DB most dev by pure C#/vb.net/F#
https://github.com/pmikstacki/SliccDB Light Embedded Graph Database for .net
https://github.com/stonstad/Stellar.FastDB Embedded document storage built for performance and high concurrency. https://github.com/FriendlyCSharp/Databases A library of cross platform C# data structures. Generic B-tree written in C#, which can be replaced with NoSQL database stored in the memory of discharge requirements in real-time (Firebase, Redis Cache, SAP HANA, Exadata, OLTP, etc.). https://github.com/pocketsol/VestPocket Single-file persisted lookup key/value database contained in a pure .NET 7.0+ library. All records persisted are kept in-memory for fast retrieval and synchronized with the file. https://github.com/cdy816/mars Mars 数据库是一个集数据采集、存储、分析为一体的实时数据库 https://github.com/Alachisoft/NosDB NosDB: Highly Scalable NoSQL Database for .NET https://github.com/cognitum-octopus/cognipy In-memory Graph Database and Knowledge Graph with Natural Language Interface, compatible with Pandas https://github.com/bitzhuwei/SharpFileDB SharpFileDB is a micro database library that uses no SQL, files as storage form and totally C# to implement a CRUD system. SharpFileDB是一个纯C#的无SQL的支持CRUD的小型文件数据库，目标是支持万人级别的应用程序。 https://github.com/VeloxDB/VeloxDB An object oriented database for building next generation solutions with .NET and C#. https://github.com/markmeeus/MarcelloDB .net/mono/xamarin/winrt in-process object database https://github.com/usinesoft/Cachalot Fastest transactional database for dotnet applications (classic or core); it can also be used as a high performance distributed cache https://github.com/DiverOfDark/ObjectRepository EscapeTeams In-Memory Object Database https://github.com/DevrexLabs/OrigoDB In-memory event-sourced database engine for NET/Mono https://github.com/nam178/FooDBYour own custom-build database Sterling NoSQL 面向对象数据库 SapphireDb Server, a self-hosted, easy to use realtime database for Asp.Net Core and EF Core
SapphireDb
https://github.com/VeloxDB/VeloxDB An object oriented database for building next generation solutions with .NET and C#. https://github.com/usinesoft/Cachalot Fastest transactional database for dotnet applications (classic or core); it can also be used as a high performance distributed cache https://github.com/Bobris/BTDB Key Value Database in .Net with Object DB Layer, RPC, dynamic IL and much more https://github.com/Cratis/Chronicle Event Sourcing database built with ease of use, productivity, compliance and software evolution in mind. https://github.com/mizrael/EvenireDB This project is a Proof-of-Concept of a small stream-based DB engine.One of the potential use cases is Event Sourcing. I https://github.com/jessiepathfinder/LesbianDB-v2.1 An ultra-simple, high-performance, work-in-progress database https://github.com/StephenCleary/ArcDb An ACID .NET relational database. More specifically, ArcDb is a disk-based, row-oriented OLTP storage engine. https://github.com/Build5Nines/SharpVector Lightweight In-memory Vector Database to embed in any .NET Applications