What is the difference between open-source and public domain software?

Open-source software and public domain software differ primarily in how they handle licensing, usage rights, and ownership. Open-source software is distributed under licenses that grant users the right to view, modify, and redistribute the source code, provided they adhere to specific conditions outlined in the license. These licenses, such as the MIT License or GNU GPL, often require derivative works to maintain the same open terms or give credit to the original authors. In contrast, public domain software is not protected by copyright at all, meaning anyone can use, modify, or distribute it without restrictions or obligations. This distinction hinges on legal ownership and the presence (or absence) of enforceable terms.

Legally, open-source software retains copyright ownership, but the license grants permissions to users. For example, the Apache License 2.0 allows commercial use but requires attribution and disclosure of modifications. Public domain software, however, has no copyright holder—either because the creator explicitly waived their rights (using tools like Creative Commons CC0) or because the copyright expired. For instance, SQLite is often cited as public domain, though it uses a custom waiver to ensure global recognition. Note that in some jurisdictions, surrendering copyright entirely isn’t legally possible, so public domain dedications often rely on fallback licenses to avoid ambiguity.

From a developer’s perspective, the choice between open-source and public domain affects flexibility and compliance. Open-source licenses like GPL can restrict how code is reused (e.g., requiring derivative projects to also be open-source), whereas public domain code imposes no such limits. This makes public domain code attractive for proprietary projects seeking unrestricted reuse. However, open-source licenses provide clearer legal frameworks, ensuring contributors retain credit and enforce collaboration rules. Developers should verify a project’s license or waiver terms to avoid unintended obligations, especially when combining code from multiple sources.