Gstring is yet another guitar tuning application. It requires a soundcard, a microphone, the FFTW package, and if you want a GUI, the Gtk+ toolkit and a new Gtk+ widget called GtkDatabox. A non- Gui version called "string" is included in version 1.0.0 and dynamically linked binaries (for i386 machines) are included as well.
GQuiz is a generic question/answer drilling program. You provide a program that displays the question and answer, given as a single filename on the command line, and gquiz randomizes, prevents immediate repetition, and temporarily eliminates questions you've answered correctly "enough" times in a row. The author uses GQuiz with cgoban to study go, the Asian strategy game, but it could just as well be used to memorize States and their Capitals, or foreign language vocabulary, etc.
Grave is an MP3 playlist editor and interface tool for the Sensory Science RaveMP MP2000 Digital Media Player, made with the GTK+ toolkit and GNOME libraries. It allows you to create and edit playlists, which are stored as text files and can be used with most (software) MP3 players (i.e. XMMS). The part interacting with the RaveMP (hardware) MP3 player can upload and download single files or complete playlists.