Jmol is a Free, Open Source molecule viewer and editor. It is a collaboratively developed visualization and measurement tool for chemical scientists. Jmol is an active project, and there are new features being added to it on a daily basis. Users are encouraged to modify it to fit their needs and to contribute their changes to the project.
There are many photo-gallery programs available. Zoph is different, as it concentrates on the management of large collection of photos instead of just showing them on the Web. It can store a lot of information about your photos, including the regular EXIF info, photographer, location, title, description, rating, and the people in the photo. Photos can appear in multiple albums and categories. Additional features include search, slideshows, lightboxes, email, access privileges, and multiple languages.
Tux Paint is a simple and entertaining drawing program geared towards young children. It has a simple interface, sound effects, and a cartoon character (Tux, the Linux penguin). Along with drawing brush strokes, lines and shapes, you can also enter text and place "rubber stamp" (or "sticker") images on the picture. Tux Paint is extensible, and could be useful in an educational environment (such as a grammar, elementary, or grade school). It's portable across numerous platforms, and runs well even on slower systems like the Pentium 133MHz.
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.
MuseScore lets you notate and compose music easily with your keyboard, your mouse, or a MIDI keyboard. You can print beautifully engraved sheet music or export it as PDF or PNG. You can play your score, transpose it, and save it as audio or MIDI file. MuseScore also supports MusicXML to let you share your composition with other scorewriters. MuseScore is often advertised as a cost effective alternative for Sibelius and Finale.
mtPaint is a simple GTK+1/2 painting program designed for creating icons and pixel-based artwork. It can edit indexed palette or 24 bit RGB images and offers basic painting and palette manipulation tools. Its main file format is PNG, although it can also handle JPEG, GIF, TIFF, BMP, TGA, XPM, and XBM files.