WinFsp is a Windows File System Proxy that provides a FUSE (Filesystem in Userspace) compatible API for Windows. It allows developers to create custom file systems in user space using C, C++, .NET, or any language that can call a C library. The repository contains a kernel-mode Windows driver (`src/sys/`) that handles IRP dispatch and communicates with a user-mode DLL (`src/dll/`) via a transaction protocol. It includes a comprehensive FUSE v2 and v3 compatibility layer, a native WinFsp API, a service launcher for running file systems as Windows services, a network provider for automatic mounting, and an extensive test suite. The architecture is a hybrid kernel/user-mode system, deeply integrated with Windows NTFS semantics. While primarily an application framework, it also contains performance benchmarking data and analysis notebooks in its documentation. The codebase is actively maintained, demonstrates high craftsmanship in a difficult domain, and contains several reusable components such as a fault injection framework, POSIX-to-Windows security mapping, and a directory buffer abstraction.
hMailServer is a production-grade, open-source email server for Microsoft Windows, implementing SMTP, POP3, and IMAP protocols with comprehensive anti-spam (SPF, DKIM, DMARC, DNSBL, SURBL, greylisting, SpamAssassin) and anti-virus (ClamAV, ClamWin, custom) capabilities. The server core is written in C++ using Boost.Asio for asynchronous I/O and exposes a COM automation API for administration. It is complemented by a .NET WinForms Administrator GUI, a PHP-based web admin, and a suite of database upgrade scripts supporting MySQL, MSSQL, PostgreSQL, and SQL Server Compact Edition. The architecture follows a layered pattern: business objects (e.g., Account, Domain, Rule) with a generic Collection/Persistence layer, a caching subsystem with TTL-based eviction, and a plugin-style spam test runner. Key data flows include message reception via SMTP, anti-spam scanning, local or external delivery, and optional virus scanning. External dependencies include OpenSSL, Boost, and database client libraries. The codebase is well-structured with reusable patterns but shows signs of age (manual memory management, COM, .NET Framework 4.5, PHP without modern framework).