Open source. Open possibilities.

FlatRedBall is a cross-platform 2D game engine built with .NET and C#, featuring a dedicated editor to enhance developer productivity.

ET is a dual-end game development framework based on Unity3D client and C# server, supporting distributed architecture, Actor messaging, coroutines, hot updates, and AI-assisted development.

An open-source developer platform for building native cross-platform .NET applications for Web, Desktop, Mobile, and Embedded systems from a single C#/XAML codebase.

Nakama is an open-source game backend server from Heroic Labs. It provides users, storage, social graph, chat, realtime and turn-based multiplayer, leaderboards, tournaments, parties, purchase validation, notifications and runtime code.

ML.NET is an open-source, cross-platform machine learning framework for .NET that lets developers build, train, deploy, and consume custom models directly in .NET apps without needing Python or R.

Kahuna is an open-source distributed systems toolkit providing distributed locking, a fault-tolerant key/value store, and globally ordered ID sequencing, built on Raft consensus and MVCC.

LiteDB is a lightweight, serverless NoSQL embedded database for .NET that stores data in a single file, offering ACID transactions, LINQ queries, and a MongoDB‑like API while remaining under 450 KB.

A strongly-typed .NET wrapper for FFmpeg and FFprobe, providing a fluent API for media transcoding, trimming, merging, and watermarking.

Read-only-by-default Model Context Protocol (MCP) server for Microsoft SQL Server, providing metadata discovery, parameterized SELECT-only queries, execution plan analysis for slow query diagnosis, profile-based multi-connection configuration, and optional per-profile write access, shipped as a .NET NuGet tool.

SMTP Tool is a portable Windows desktop application for testing, diagnosing, and debugging SMTP servers. It supports TLS 1.3, real-time open/click tracking via local HTTP server, latency benchmarking, and interactive protocol terminal.

A Windows desktop utility for managing and switching authentication accounts for AI coding tools like Codex and Claude Code. It provides a GUI to add accounts, switch active credentials, monitor usage quotas, and display real-time usage in the taskbar.

A transport-agnostic OAuth 2.1 and OpenID Connect server built on OpenIddict and redb.Route, supporting multiple databases, MFA, WebAuthn, SCIM, and in-process direct-vm calls.

rzeka is a single-threaded reactive event bus for C# built on Rx.NET that features automatic causality tracking and a real-time browser-based debugger.

Soenneker.Loops.Contacts is a .NET utility library for managing Loops contacts by email. It provides create, update, find, and delete operations, configuration through a Loops API key, and scoped or singleton dependency injection registration.

BarakoCMS is a headless, API-first CMS suite for .NET 10 featuring an event-sourced engine, multi-tenancy, and a modular architecture.

optimizerDuck is a free, open-source Windows optimization tool for performance, privacy, and simplicity. It offers 42 tweaks, 44 customization settings, and built-in tools like startup manager and disk cleanup, with automatic backups and one-click revert.

TUnit-native math assertion library for .NET: fluent tolerance, sequence, statistics, linear algebra, number theory, and 3D geometry assertions generated into TUnit's Assert.That pipeline; AOT-compatible and reflection-free.

A .NET library for multi-tenant SQLite: per-tenant file isolation or shared-schema scoping, integrity checks across tenants, tenant context helpers, rate limiting and error middleware validation, plus settings and JSON utilities.

Technitium DNS Server is an open-source authoritative and recursive DNS server for self-hosting, featuring ad/malware blocking, encrypted DNS protocols (DoT/DoH/DoQ), DNSSEC, a web console, and clustering support.

Microsoft Agent Framework (MAF) is an open-source framework for building production-grade AI agents and multi-agent workflows in Python, .NET, and Go. It supports orchestration patterns, multiple LLM providers, observability, and deployment to Microsoft Foundry.