There are at least these three packages in the Ubuntu repositories:
ll-scope - an oscilloscope DSSI plugin
The Oscilloscope is a DSSI plugin with a GUI that displays the audio input in an oscilloscope view. It can be useful when working with modular synths, to view the waveforms with at different places in the synth graph.
wmscope - Graphical representation of sound waves in a dockapp
wmscope is a dockapp that displays sound waves graphically, reading from a variety of sources. It also has a standby sine wave interference pattern to display when there is no audio input.
xoscope - digital oscilloscope
Xoscope is a oscilloscope using input from a sound card or EsounD and/or a ProbeScope/osziFOX and will soon support Bitscope hardware. Includes 8 signal displays, variable time scale, math, memory, measurements, and file save/load.