FB-Mix is designed to sit in the Fluxbox system tray and popup an alsamixer window when clicked. It should also work with other window managers. As of version 0.2, volume can also be adjusted using the mouse scrollwheel when hovering over the icon.
VU meter plugin is a visualization plugin that works with both XMMS and Audacious. The plugin is mostly for eye candy, though it shows dBFS levels of sound, at least to a point.
Tiny, portable general Unix utilities.
Protocol Buffers for R6RS Scheme.