WeasyPrint is a production-grade Python library and CLI that renders HTML/CSS documents to PDF with high fidelity to print-focused web standards. In production it parses HTML via tinyhtml5, parses and validates CSS via tinycss2/cssselect2, builds a CSS box tree, runs full CSS layout algorithms for block, inline, table, flex, grid, multicolumn, floats, and paged media, then paints the result into a PDF via pydyf. It also renders embedded and standalone SVG, embeds and subsets fonts through Pango, HarfBuzz, Fontconfig, and fontTools, and supports PDF/A, PDF/UA, PDF/X, PDF forms, attachments, bookmarks, metadata, and e-invoice flavors such as Factur-X/ZUGFeRD. The main entry points are the `weasyprint` command-line tool (`weasyprint/__main__.py`) and the public Python API exposing `HTML`, `CSS`, `Document`, and `Page` (notably `HTML(...).write_pdf(...)`). Architecturally the repository is a layered pipeline rather than a monolith or microservice: CSS property validation and computed-value resolution feed a formatting-structure builder, which produces boxes; those boxes go through layout modules that handle pagination and page-breaking; a drawing layer converts the laid-out box tree into PDF stream operations; and the PDF package assembles final file objects, metadata, and conformance variants. The code is heavily specification-driven, with many docstring references to CSS 2.1, CSS Paged Media, CSS Flexbox/Grid, SVG, and PDF standards. Extensive pixel-comparison tests, regression tests tied to GitHub issues, and CI workflows for PDF/A and PDF/UA validation back the implementation. External runtime dependencies include pydyf, tinyhtml5, tinycss2, cssselect2, Pyphen, Pillow, fontTools, and native Pango/HarfBuzz/Fontconfig libraries; Ghostscript is used only by the test suite for rendering comparisons. The codebase is mature and generally well-structured, with clean separation between CSS processing, layout, drawing, and PDF output. It contains some inevitable complexity around pagination, table layout, and font handling, plus a set of `xfail` tests and TODO comments marking known spec coverage gaps, but overall it is one of the strongest open-source HTML-to-PDF engines and is actively maintained with recent security fixes and broad standards support.

Radicale is a production-grade CalDAV and CardDAV server implemented in Python. It provides a self-hosted solution for managing calendars, address books, tasks, and journals via standard WebDAV, CalDAV, and CardDAV protocols. The system supports multi-user, multi-collection setups with pluggable backends for authentication (htpasswd, LDAP, IMAP, OAuth2, PAM, Dovecot, remote_user), storage (multifilesystem with caching), rights management, sharing (token/map-based), and web UI. It includes a built-in HTTP/HTTPS server with WSGI compatibility, a browser-based management interface, and extensive configuration options for security, performance, and integration with reverse proxies. The architecture follows a modular plugin pattern: each major subsystem (auth, storage, rights, web, hook, sharing, group) defines a base class and is loaded dynamically via a plugin loader. The core application dispatches HTTP requests through a WSGI application class that handles authentication, locking, logging, and profiling. The storage layer uses a mixin-based design to separate concerns (cache, sync, history, lock, etc.) and stores collections as filesystem directories with individual item files. The sharing module provides a REST API for managing shares, including VCF-to-ICS birthday conversion and property overlays. Key features include CalDAV filtering and recurrence expansion, sync-token support, free-busy reports, email notifications via hooks, and a JavaScript frontend for collection and sharing management. The codebase is well-tested with both unit tests (Python) and integration tests (Playwright), and includes CI/CD pipelines for multi-architecture Docker images and PyPI publishing. While primarily an application, it contains reusable data processing logic for iCalendar/vCard parsing and transformation.