Apache Nutch is a web crawler that is open-source and designed to efficiently gather and index large web content volumes. Its architecture is highly extensible, enabling developers to craft custom plugins for various tasks like data retrieval, parsing, and indexing. Supporting distributed crawling, Nutch integrates well with other Apache projects such as Hadoop and Solr for enhanced data processing and search functionalities. This makes it suitable for both small-scale and large-scale applications.