"Apache CouchDB is a distributed, fault-tolerant and schema-free document-oriented database accessible via a RESTful HTTP/JSON API. Among other features, it provides robust, incremental replication with bi-directional conflict detection and resolution, and is queryable and indexable using a table-oriented view engine with JavaScript acting as the default view definition language." Written in Erlang, for extra fun .
"Nutch is open source web-search software. It builds on Lucene Java, adding web-specifics, such as a crawler, a link-graph database, parsers for HTML and other document formats, etc."
Apache Maven's reuse mechanisms simplify the build process and generally improve upon the popular Ant tool's functionality. In fact, developer and Java technology trainer Dave Ford believes Maven could very well replace Ant as your preferred Java build tool.
mod_auth_tkt is a lightweight cookie-based authentication module for Apache, written in C. It implements a single-signon framework that works across multiple apache instances and multiple machines.