QueryFS is a FUSE-based virtual filesystem that is based on queries. There are plugins to parse various query syntaxes and each query creates a virtual directory. Currently the most elaborate query language is SQL-based; you can either provide access to data stored in an SQL database, or keep an index of files in the SQL database and generate search directories with symlinks to found files. QueryFS and its SQL2 query DSL fully support creation of refinable searches: for example, the author has an index of downloaded email files; one can see all the distinct senders registered in the DB and then go into a directory of one sender and see all accounts that ever received an email from this sender.
g7ctrl is a daemon and a command shell that are used together with the Xtreme GM7 GPS tracker to help simplify its management and to make it possible to monitor alerts sent by the tracker. It is designed to run in the background and can be used to both receive location updates from a remote tracker and configure a tracker over USB. All received events are stored in a database and can be exported to GPX, KML, and CSV, with distances calculated. It can also execute action scripts upon receiving specific events or generate mail notifications. Extensive reference documentation (HTML and PDF) and Unix man pages are provided.