SQLite

SQLite is a C-language library that provides a lightweight, self-contained SQL database engine with no external dependencies or separate server process. It is embedded directly into applications and is the most widely deployed database engine in the world, found in virtually all mobile phones and most computers.

Source: https://www.sqlite.org

Yes. SQLite's source code is placed in the public domain by its authors and contributors. Anyone is free to copy, modify, use, compile, and distribute SQLite for any purpose—commercial or non-commercial—without requiring permission or payment.

Source: https://www.sqlite.org/copyright.html

SQLite is designed as a replacement for file input/output operations like fopen() and fread(), not as a replacement for enterprise database servers like Oracle or PostgreSQL. It is optimized for storing structured data within applications with minimal overhead and configuration.

Source: https://www.sqlite.org/about.html

SQLite excels for embedded applications, mobile devices, local desktop applications, and low-to-medium traffic websites (under roughly 100,000 hits per day). Use a client-server database like PostgreSQL or MySQL if your application requires multiple concurrent writers, network database access, or extreme scalability.

Source: https://www.sqlite.org/whentouse.html

SQLite allows only one writer at a time, though multiple readers can work concurrently. Databases can theoretically reach 281 terabytes in size and support rows up to 1 gigabyte, though most deployments are considerably smaller and single-file-based.

Source: https://www.sqlite.org/about.html

SQLite is highly reliable with ACID transaction support and aviation-grade testing including 100 percent branch coverage. It recovers cleanly from power failures and system crashes, making it suitable for critical embedded applications, though its single-writer model makes it unsuitable for high-concurrency server environments.

Source: https://www.sqlite.org/about.html

SQLite provides a C API for direct integration and is widely supported by bindings in nearly every major programming language, including Python, JavaScript, Java, C#, Ruby, PHP, and others. Its public domain status allows libraries to be created for any language or platform.

Source: https://www.sqlite.org