Firestarter is a firewall tool for Linux, and uses GNOME. You can use the wizard to create a basic firewall, then streamline it further using the dynamic rules. You can open and close ports with a few clicks, or stealth your services giving access only to a select few. It features a real-time hit monitor which you can watch as attackers probe your machine for open ports.
The Bubbling Load Monitor (or "Bubblemon" for short) is a system load monitor for the GNOME panel. It looks like a vial containing water. The water level indicates how much (electronic) memory is in use. The color of the liquid indicates how much swap space is used. The amount of bubbles reflects the system CPU load. A message in a bottle indicates there is unread mail. A reed-like graph shows I/O load. On multi-core systems the CPU with the highest load will bubble in the middle, and the others on the sides, so it's possible to see how well load gets distributed between CPUs.
audio convert is a script that converts between WAV, Ogg, MP3, MPC, FLAC, APE, AAC, and WMA files. It has an easy-to-use interface that makes it possible to fill in the tags for a few formats, copy the tags from input files into the new files, and choose the quality of compression. The script was initially designed for the Nautilus file browser and can be easily installed into Nautilus by using the installer provided with the script. You can then right-click on files and choose "audio-convert" from the "scripts" menu. The script is also known to work on rox or directly from a shell.
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.
Cheops-ng is a network management tool for mapping and monitoring your network. It has host/network discovery functionality and OS detection, and does a port scan of each computer to tell what services are running. It can probe FTP, HTTP, ssh, email (port 25), news, IMAP, and VNC to see what version and type of server is running on those ports.