Subversion is a version control system. Originally designed to be a compelling replacement for CVS in the open source community, it has far exceeded that goal and seen widespread adoption in both open source and corporate environments. The Subversion project produces Subversion's core libraries (written in C), a fully functional command line client (svn), repository administration programs, API bindings for various languages (Perl, Python, Java, Ruby, etc.), and various additional tools and scripts.
Apache SpamAssassin is an extensible email filter that is used to identify spam. Once identified, the mail can then be optionally tagged as spam for later filtering. It provides a command line tool to perform filtering, a client-server system to filter large volumes of mail, and Mail::SpamAssassin, a set of Perl modules allowing Apache SpamAssassin to be used in a wide variety of email systems.
OrientDB is a NoSQL DBMS which can store 150,000 documents per second on common hardware. Even with a document-based database, the relationships are managed as in graph databases, with direct connections among records. You can traverse entire or parts of trees and graphs of records in a few milliseconds. It supports schema-less, schema-full, and schema-mixed modes, has a strong security profiling system based on users and roles, and supports SQL between the query languages. Thanks to the SQL layer, it's straightforward to use for people skilled in the relational world.
Piggydb is a flexible and scalable knowledge building platform that supports a heuristic or bottom-up approach to discover new concepts or ideas based on your input. You can begin with using it as a flexible outliner, diary or notebook, and as your database grows, Piggydb helps you to shape or elaborate your own knowledge. Piggydb is a Web application provided as a self-contained package that contains a Web server and database engine.
Monkey HTTP Daemon is a very fast and lightweight Web server for Linux. It uses a hybrid networking model based on asynchronous calls (event-driven) and fixed threads, which makes it scalable and capable of attending thousands of clients per second. It provides a powerful API for C and is ideal for embedded devices, thanks to its small core and plugin architecture.
Apache OpenMeetings is a multi-language customizable video-conferencing and collaboration system. It supports audio/video and allows you to see the desktop of any participant. It includes a whiteboard, the ability to import a variety of image formats, invitations, a moderation system, backup and language modules, private and public conference rooms, and the ability to record meetings. The project also provides integrations for Asterisk, Jira, Confluence, Moodle, Sakai, and SugarCRM, and connectors for LDAP and ADS.