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.
gRio500 is a Gnome/GTK program that lets you interface with the Rio500 MP3 player by Diamond/S3/SonicBlue. You can currently create/delete folders, add/delete songs, format memory, rename folders/songs, automatically downmix/resample MP3s during transfer, and preview MP3s (play/stop controls). You can interface with both internal and external memory (Smartmedia).