fontspec is a mature LaTeX package that provides an automatic and unified interface for font selection in XeLaTeX and LuaLaTeX. It allows users to load OpenType, AAT, and Graphite fonts by name or filename, with full control over features such as ligatures, small caps, numerals, script/language selection, colour, scaling, and more. The architecture is modular: a core LaTeX3 (expl3) implementation wraps engine-specific code (XeTeX primitives or luaotfload) behind a consistent key-value interface, and provides both user commands (`\setmainfont`, `\fontspec`) and a programmable API (`\fontspec_*` conditionals) for other packages. The codebase is structured as literate `.dtx` files, generating both the package `.sty` files and comprehensive documentation. It includes an extensive test suite with over 100 test files that run on both XeTeX and LuaTeX, a fully automated CI/CD pipeline (testing, documentation, release), and is distributed on CTAN under the LPPL 1.3c license. The package is actively maintained by the LaTeX3 Project team, tracking OpenType specification updates and TeX engine changes, though its dual-engine support and large static data tables (language/script mappings) introduce some maintenance overhead.
Tectonic is a modernized, self-contained TeX/LaTeX engine that compiles .tex documents to PDF or HTML. It is built on a fork of XeTeX and integrates BibTeX, font shaping via HarfBuzz/FreeType, SVG-to-HTML conversion, and full PDF output via xdvipdfmx. The architecture is a Rust workspace with multiple crates implementing engines, I/O abstraction, bundle management, and C library bridges. The CLI tool provides subcommands (build, watch, new, bundle, dump, show) and supports workspace configuration via Tectonic.toml. The system is production-ready, with extensive test coverage, fuzzing, and support for cross-compilation. While the core TeX engine remains in C/C++ with global state, the Rust layers provide clean abstractions (IoProvider, StatusBackend, CachableBundle) that are reusable and well-architected. The codebase is actively maintained, with regular commits and CI/CD pipelines, though some C components show age and legacy patterns.
MiKTeX is a comprehensive, cross-platform TeX distribution that provides a complete typesetting system for Windows, macOS, and Linux. The repository contains the source code for TeX engines (pdfTeX, XeTeX, LuaTeX, e-upTeX, etc.), companion tools (dvipdfmx, dvisvgm, asymptote, metapost, tex4ht, etc.), the TeXworks editor, and the MiKTeX package manager (Console) and DVI viewer (Yap). It also bundles a large number of third-party libraries (FreeType, HarfBuzz, Poppler, LibreSSL, cURL, GMP, MPFR, etc.) as vendored dependencies. The architecture is monolithic: each executable compiles independently but shares a common core library (MiKTeX Core) that provides session management, file I/O, package management, and platform abstraction. The primary data flow is user-driven: packages are downloaded from remote repositories, TeX documents are compiled via one of the engines producing DVI or PDF output, and fonts are handled via system or bundled resources. The codebase is actively maintained with frequent releases, but the reliance on many vendored libraries and extensive platform-specific `#ifdef` blocks introduces moderate technical drift risk.