Which database is best for a development team looking for a document-oriented, open-source solution?

Selecting the most suitable database for a development team aiming for a document-oriented, open-source solution leads to MongoDB as the ideal choice. MongoDB is specifically designed to manage and store data in a flexible document format that supports various data types, making it particularly effective for applications that require the handling of unstructured data or complex queries.

As a NoSQL database, MongoDB allows for horizontal scaling and offers high availability, which is vital for modern applications that expect rapid growth and varying workloads. Its capability to store data in a format similar to JSON (JavaScript Object Notation) means that developers can easily work with the data without needing to adhere to a rigid schema, thus accelerating the development process.

The other options provided do not serve the purpose of a document-oriented database. REST is an architectural style for designing networked applications, which is not a database solution. Browser extensions are tools that enhance web browsers and do not pertain to database functionalities. HTML5, while relevant for structuring content on the web, is not a database but rather a markup language used for building web applications. Therefore, MongoDB stands out as the best option in this context.