SQLet allows you to directly execute SQL on multiple text files, right from the Linux commandline. In one single command, you can read in text files (with or without header lines) and perform arbitrary select statements, including joins over several files. SQLet can thus replace awk or grep in some instances.
WaldScan is a PHP class which recursively scans a given directory for a list of selected file types. It has many uses for any Web page which serves files over HTTP/HTTPS, for a CLI program which does batch processing of files, or in cron jobs for caching file data for faster access.
HTSQL a high-level query language and Web service gateway for relational databases. It comes with source code and is royalty free for any use with open source database systems such as MySQL, PostgreSQL, SQLite, etc. Licenses for using HTSQL in conjunction with proprietary databases such as Microsoft SQL and Oracle can be purchased.
Goggles Music Manager is a music collection manager and player that automatically categorizes Ogg Vorbis, FLAC, MP3, MP4, ASF, and Musepack files based on genre, artist, album, and song. It supports gapless playback, features easy tag editing, and allows scrobbling tracks to last-fm.
Klen-library is a program for creating electronic books. It consists of three modules, for editing books, reading books, and creating tests. It offers password protection of every book and the editing mode. The print function makes it self-sufficient, as it allows creation of books without using third-party text editors. It uses SQLite, so you don't have to install a database server. It can export to the XWB, HTML, TXT, PDF, PostScript, and RTF formats, and can import from XWB, HTML, and TXT.
Lyra is a front-end to the Music Player Daemon (MPD). Based loosely on the Creative Media Source software, it has the aim of supporting large collections of albums and artists. Other interesting features are the implementation of a local cache of the music library using an SQLite database, increased speed, and flexibility. In addition, Lyra supports integration with the Last.fm service, which includes "Scrobbling" and album cover art.