HyperSQL is like the doxygen program with Javadoc added, but for SQL. It hypermaps SQL views, packages, procedures, and functions to HTML source code listings, and it shows all the code locations where these are used. You can use JavaDoc-style comments for documentation and even embed UnitTests with them.
mod_musicindex is an Apache module aimed at being a C alternative to the Perl module Apache::MP3. It allows nice displaying of directories containing MP3, Ogg Vorbis, FLAC, or MP4/AAC files, including sorting them on various fields, streaming/downloading them, constructing playlists, and searching. It also provides features such as RSS and Podcast feeds, multiple CSS support, and archive downloads.
Alexandria is a GNOME application to help manage a book collection. It retrieves book information (including cover pictures) from several online libraries, allows you to search for a book (either by EAN/ISBN, title, authors, or keyword), can import and export data into ONIX, Tellico, and EAN/ISBN-list formats, generates Web pages from your libraries, allows marking your books as loaned, saves data using the YAML format, features an HIG-compliant user interface, shows books in different views that can be filtered or sorted, and handles book rating and notes.
YaCy is a search engine that anyone can use to index the Internet (WWW and FTP) or to create a search portal for others (Internet or intranet). The scale of YaCy is limited only by the number of users. and can index billions of web pages. In P2P mode it is fully decentralized. All users of the search engine network are equal and it is not possible for anyone to censor the content of the distributed index.
Lease Parser saves lease states from an ISC DHCP server in a MySQL database, making it possible to tell which MAC address owned an IP at a particular time. If you need to track down a DHCP user for any reason, such as an abuse complaint for actions weeks beforehand, you can simply search the database via the Web form for the IP during the time in question. Then, search on the MAC address you obtained to see if the system is still on the network and what it's current IP is.