Gentoo Linux is a versatile and fast Linux distribution for x86, PowerPC, Sparc, and Sparc64 that's geared towards Linux power users. Unlike other distros, it has an advanced package management system called Portage. Portage is a true ports system in the tradition of BSD ports, but is Python-based and sports a number of advanced features including dependencies, fine-grained package management, "fake" (OpenBSD-style) installs, path sandboxing, safe unmerging, system profiles, virtual packages, config file management, and more.
Gfract is a GTK-based fractal program that implements the standard Mandelbrot and Julia sets. It features infinite image size with infinite anti-aliasing if you have the memory for it, Julia instant preview mode, user-specified coloring algorithms, and PNG support. For palette files it uses the same format as Fractint does, except that it supports arbitraly large palettes.
gFTP is a free multithreaded file transfer client for *NIX based machines running X11R6 or later. It has text and GTK+ 1.2/2.x interfaces and supports the FTP, FTPS (control connection only), HTTP, HTTPS, FSP, and SSH protocols and has FTP and HTTP proxy server support. It supports UNIX, EPLF, Novell, MacOS, VMS, MVS, and NT (DOS) style directory listings, and has a bookmarks menu that allows you to quickly connect to remote sites. The code is fully internationalized and there are currently 45 translations available.
Ghemical is a molecular modelling software package with some nice 3D visualization tools. It supports methods based on both molecular mechanics and quantum mechanics (using MOPAC7, and MPQC for QM). The geometry optimization (for MM and QM) and molecular dynamics (for MM) algorithms are included. Ghemical is written in C++, and hopefully offers a good framework for a generic freeware molecular modelling tool.
Gibraltar is a Debian GNU/Linux-based router/firewall distribution, fully workable from a bootable, live CD-ROM. Log files can be stored on a hard disk, and configuration data is stored on a USB mass storage media or a floppy disk and kept on a RAM disk during run-time. Due to its Debian base, a vast manifold of firewalling, routing, and proxy packages is available. It comes with an intuitive, easy to use Web administration interface and support, and is free to use for home users.