Waveforms is free to download, and is available for Windows, Mac and Linux (although it is only installed on Windows machines at CAE).
http://www.digilentinc.com/Products/Detail.cfm?NavPath=2,66,849&Prod=WAVEFORMS&CFID=6529835&CFTOKEN=de25659007ebda6-1165B989-5056-0201-023471C06D655FCE

WaveForms is a powerful suite of virtual instruments that brings analog and digital circuit design to your PC desktop. WaveForms seamlessly connects to our Analog Design products, such as the Electronics Explorer™ board and the Analog Discovery™ Kit. WaveForms provides a clean, easy to use graphical interface for each instrument, making it easy to acquire, store, analyze, produce, and reuse analog and digital signals.