G-Force is a free visualizer plug-in for iTunes, which extends your options beyond iTunes' built-in visualizers for displaying colorful light shows to accompany your music. You activate G-Force like any other visualizer, just by selecting it while in iTunes, and then it shows complex, constantly changing visuals that move and react to whatever music you're playing. Because G-Force combines a huge number of shapes, colors, images, and other variables, this app produces millions of possible visual effects. What makes G-Force more interesting than many visualizers is hotkeys for quickly adjusting visuals on the fly (like skipping through effects or adjusting pixel doubling and line boost) and the ability to customize playback, by adding user images, running custom scripts, and even building themes. Unfortunately, there isn't a user-friendly interface for these customization features, but anyone willing to explore G-Force's preference files will find unlimited possibilities for tweaking and tinkering.