Tax-Calculator is a mature, open-source microsimulation library for static (and simple behavioral) analysis of the US federal individual income and payroll tax system. It provides a Python API and a CLI tool (`tc`) that allow users to define policy reforms via JSON parameter files, apply them to microdata samples (CPS, PUF, or TMD), and produce distributional tables, revenue estimates, marginal tax rates, and welfare measures. The core architecture separates policy parameters (`Policy`), taxpayer records (`Records`), and economic adjustments (`GrowFactors`, `GrowDiff`, `Consumption`) from the calculation engine (`Calculator`), which uses Numba JIT compilation for performance. While primarily an application/library with formal releases and CI/CD, it also bundles research data (CPS microdata, grow factors) and includes extensive cross-validation against NBER's TAXSIM-35 model. The codebase is well-structured, heavily tested, and actively maintained, with a clear modular design that supports both CLI and programmatic use.
Akaunting is a self-hosted accounting and invoicing platform for small businesses and freelancers. It manages invoices, bills, banking transactions, transfers, reconciliations, multi-currency, multi-tax, recurring documents, and financial reports. It includes a customer portal for invoice viewing and payment, and supports multi-company, multi-user with role-based permissions. The system is highly internationalized with 40+ language locales. The architecture is built on a custom PHP framework (Illuminate) that extends Laravel conventions. It uses an event-driven architecture with domain events, listeners, and a job queue for async processing. The frontend combines Blade templates, Vue.js components, and Livewire for interactivity. Multi-tenancy is achieved through company scoping via a global query scope. The system is extensible via a module system with an app store, and includes a CLI for maintenance tasks. Key entry points include the installation wizard (controllers under Install/), authentication flows, and core CRUD controllers for sales, purchases, banking, and settings. Data flows typically involve controllers dispatching jobs that emit events, which listeners handle to update related entities, send notifications, or trigger side effects. Reports use a filter/group/rows event system for extensibility. Import/export is handled via Excel with multi-sheet support. External dependencies include PHP 8.1+, Node 18-20, and a database (MariaDB, MySQL, PostgreSQL, SQLite). It uses Laravel Mix for asset compilation, integrates with payment gateways, email services, and error trackers (Sentry, Bugsnag), and relies on a module marketplace at api.akaunting.com.
Firefly III is a self-hosted personal finance management application built on the Laravel PHP framework. It provides comprehensive double-entry bookkeeping with support for multiple currencies, accounts, budgets, categories, bills, piggy banks, recurring transactions, and rules. The system exposes both a full web UI using Blade templates and Alpine.js (with legacy jQuery components) and a RESTful JSON API (v1) for programmatic access. Key features include transaction splitting, budget limits, auto-budgeting, rule-based transaction processing, exchange rate management, webhook integration, multi-user with group administration, and detailed reporting with charts. The codebase follows a repository pattern with interfaces, uses events and listeners for side effects, and includes a substantial set of artisan commands for maintenance, upgrades, and data corrections.