The Sound Guy has released Backwards Machine, a cross-platform plug-in that reverses continuous audio in real-time.

Backwards Machine includes three effects:

1. Reverse Playback: Reverses and overlaps snippets of the incoming audio, to produce an ongoing backwards effect.
2. Forward Backwards: Smoothly cross-fades between forward and backward versions of the incoming audio.
3. Reverse Repeat: Plays snippets of the input audio backwards, twice; the second time, a slight vibrato is added.

Backwards Machine supports the VST format for Windows and VST and Audio Unit formats for Mac OS X Universal Binary. It costs $35. Demos are available.