Xapian is a search engine library, scalable to collections containing hundreds of millions of documents. It's written in C++ with bindings for Perl, Python, PHP, Java, Tcl, C#, Ruby, and Lua. It is a highly adaptable toolkit that allows developers to easily add advanced indexing and search facilities to their own applications. It supports the Probabilistic Information Retrieval model and also a rich set of boolean query operators. Omega is a Web search application built upon the Xapian library. It can index a Web server's document tree (including HTML, PDF, OpenOffice, MS Word/Excel/Powerpoint/Works, WordPerfect, RTF, PS, etc.), or data exported from arbitrary sources (e.g. SQL databases).
The Apache Traffic Server (TS or ATS) is a modular, high-performance reverse proxy server, generally comparable to Squid. It was created by Inktomi, and distributed as a commercial product called the Inktomi Traffic Server, before Inktomi was acquired by Yahoo!. Traffic Server has been actively used inside of Yahoo for over 4 years, serving billions of requests every day. As of fall 2009, Traffic Server is an Open Source project, and in April 2010 the Apache Traffic Server was promoted to a top-level project of the ASF.
CGILua is a tool for developing dynamic HTML pages and manipulating input data from forms. It uses the interpreted language Lua for codifying its scripts. It has been on the road for almost 8 years now, being used in many Web products and sites. It is extensible through Lua libraries and dynamic loading of C/C++ libraries. Scripts can be written as Lua programs or HTML templates (HTML with Lua code embedded). Scripts are platform-independent.
Sputnik is a content management system (CMS) designed for extensibility. It works as a wiki out of the box, but can be extended into other things. It offers editable nodes, history and diff, user accounts with optional email validation, a flexible permission system, RSS feeds, and more. Sputnik supports access control and has editable templates. It can be used to maintain a personal Web site that doesn't look like a wiki and that only you can edit. Sputnik is easy to install on shared hosting without root accounts.