free, open-source databases

Based on community licenses (like MIT, Apache 2.0, or BSD)

• PostgreSQL: Fully free under the PostgreSQL License (similar to BSD/MIT). You can use, modify, and distribute it for any purpose, including commercial projects, without fees.
  👉 Official PostgreSQL Website [1, 2, 3, 4, 5]
• SQLite: Dedicated entirely to the public domain. It is completely free for anyone to use for any purpose, commercial or private, with zero restrictions.
  👉 Official SQLite Website [1, 2, 3, 4, 5]
• Milvus: Fully open-source under the Apache 2.0 license, making it free for enterprise AI and production pipelines.
  👉 Official Milvus Website [1, 2, 3, 4, 5]
• Qdrant: A fast and reliable vector similarity search engine written in Rust under the Apache 2.0 license.
  👉 Official Qdrant Website [1, 2, 3, 4, 5]
• Weaviate: A user-friendly, open-source vector database using the BSD 3-Clause license for its core engine.
  👉 Official Weaviate Website [1, 2, 3, 4]
• Chroma: An open-source, AI-native embedding database using the Apache 2.0 license.
  👉 Official Chroma Website [1, 2, 3, 4, 5]