Open Source C# Projects
C# is a modern, statically typed programming language used to build web services, desktop applications, games, command-line tools, and cloud software. Its features support clear, maintainable code and help catch many errors during development. With a managed runtime and broad ecosystem of libraries, C# can serve both small utilities and large applications across different operating systems and deployment environments.
Open source C# tools include application frameworks, libraries, developer utilities, servers, and games. When choosing one, consider its license, documentation, release history, community activity, supported runtime versions, platform requirements, and compatibility with your existing code. C# projects can be useful to individual developers, teams, organizations, and learners building or maintaining software in the language.
30 repositories · updated October 15, 2026
RLM: Process Large Documents in LLM-Sized Chunks
RLM is a .NET CLI for breaking large documents into manageable chunks, processing them across multiple turns, and combining the results. It suits developers using Claude Code or scripts to work with content that exceeds an LLM's context window.
QuietHealth 25/100
model-harness: Build Controllable AI Agents for .NET
A ports-and-adapters framework for building bounded, extensible AI agents in .NET. It combines a model loop with context-shaping guides, safety sensors, tools and budget controls, with adapters for Anthropic, Azure OpenAI and Ollama.
NewHealth 54/100
ContextTax: Measure MCP Tool Costs in an AI Context Window
ContextTax is a cross-platform CLI that measures how much MCP tool schemas and responses consume from an AI agent’s context window. Use Anthropic token counting for ground-truth figures or an offline estimate when you do not have an API key.
QuietHealth 20/100
Koshi: Give AI Coding Agents Local Memory and Retrieval
Koshi is a local-first MCP server for giving AI coding agents durable project memory, code retrieval, and shared team decisions. It suits teams that want context to persist across sessions and machines without relying on cloud services or API keys.
QuietHealth 24/100
mcp-server-excel: Automate Microsoft Excel with AI
mcp-server-excel lets AI assistants and coding agents automate the real Microsoft Excel application through MCP or a CLI. It suits Windows users who need workbook operations that file parsers cannot perform, such as refreshing Power Query or running VBA.
ActiveHealth 74/100
awesome-dotnet: Find .NET Libraries, Tools, and Frameworks
A community-maintained directory of .NET libraries, tools, frameworks, and software, organized by topic. Use it to discover options across areas such as APIs, databases, testing, UI, and game development.
QuietHealth 39/100
OpenRA: Play and Mod Classic Westwood RTS Games
OpenRA is a cross-platform C# engine for playing and creating real-time strategy games inspired by early Westwood classics. It supports distributed reimaginings of Red Alert, Tiberian Dawn, and Dune 2000, plus custom maps and mods.
ActiveHealth 65/100
OfficeCLI: Create and Edit Office Files from the Command Line
OfficeCLI is a cross-platform CLI for AI agents and developers to create, read, edit, and validate Word, Excel, and PowerPoint files. It combines structured commands, JSON output, and built-in document previews in a self-contained binary.
ActiveHealth 61/100
QuestPDF: Generate PDF Documents with C#
QuestPDF is a C# library for creating structured PDF documents through a fluent, component-based API. It suits .NET developers building reports, invoices, and other data-driven documents without relying on HTML-to-PDF conversion.
ActiveHealth 61/100
Lean: Build and Run Algorithmic Trading Strategies
QuantConnect Lean is an event-driven engine for developing, backtesting, and live trading algorithmic strategies across financial markets. It suits quantitative developers who want a modular C# engine with Python support and local or cloud-assisted workflows.
ActiveHealth 74/100
skills: Add .NET Skills to AI Coding Agents
A curated collection of portable skills and host-specific agents for .NET and C# coding agents. It helps agents handle development, testing, upgrades, diagnostics, and other specialized .NET tasks.
ActiveHealth 69/100
DnsServer: Run a Self-Hosted DNS Server
Technitium DNS Server is a cross-platform DNS server for recursive resolution, authoritative hosting, and network-wide filtering. It suits home labs and organizations that want control over DNS, encrypted upstreams, and a browser-based management console.
ActiveHealth 54/100