Alkaline is a full-featured standalone search and index server. The spider is a fully remote indexing daemon which includes support for all standards like robots.txt and "skip" meta tags, and allows multiple distinct configurations and search groups (searching many different sites from your server), including complex regexp indexing paths, authentification, filters for various document formats, XML-based online management and statistics, mrtg-compatible perf numbers, and more.
ASPseek is an Internet search engine, written in C++ using the STL library. It consists of an indexing robot, a search daemon, and a search frontend (CGI or Apache module). It can index as many as a few million URLs and search for words and phrases, use wildcards, and do a Boolean search. Search results can be limited to time period given, site, or Web space (set of sites) and sorted by relevance (PageRanks are used) or date. It is optimized for multiple sites (threaded index, async DNS lookups, grouping results by site, and Web spaces), but can be used for searching one site as well. It can work with multiple languages/encodings at once (including multi-byte encodings such as Chinese) due to optional Unicode storage mode. Other features include stopwords and ispell support, a charset and language guesser, HTML templates for search results, excerpts, and query words highlighting.
cthumb allows you to create Web albums of digital pictures with thumbnails, captions, and several different views of the collection, including (optionally) several languages and resolutions. An album is composed of a series of pages, each composed of a collection of pictures. You can have several annotations per picture, and can customize almost everything in the way the albums look on the screen.
Deadman's Redirect is designed to replace whatever is loaded when you click on the Home button in your browser. It is a Web surfer's power tool that can be completely customized, using HTML, to fit the needs of the user. It allows for URL redirection as well as an interface to various search engines through its aliasing system. It also supports user-set aliases with functional arguments, RSS headlines, and a history of all the URLs that pass through it.
DirList is a user directory system that runs as a CGI to serve up user lists, search for various user attributes, view their web sites, define personalised user attributes, and keep it all synchronized automatically with the underlying operating system's user database on periodic intervals with cron.
Enzyme is an architecture for creating user-searching-user applications. Right now, it is primarily useful as a resume create/search and HR management system. However, it's potential uses are wide-ranging, and it offers PHP developers an alternative to relying on simple "keyword" searching systems.
eXist is a native XML database featuring efficient, index-based XPath query processing, extensions for keyword search, XUpdate support, and tight integration with existing XML development tools. The database is lightweight and may be easily deployed in a number of ways, running either as a stand-alone server process, inside a servlet engine, or directly embedded into an application.