Xoscillo is free oscilloscope software that acquires data using an arduino (with custom firmware) or a Parallax USB Oscilloscope. Aguaviva is developing this project to support more platform.
This C#-based application features frequency analysis using FFT, auto detects the hardware, load and save waveforms, zoom in and out, open several waveforms at the same time, and ability to run several oscilloscopes simultaneously. This scope software works on Windows and Linux operating system. Download XOscillo here.