Video Delay plugin for Quartz Composer. Uses a map image to apply varying delay across the output. The download includes a qcFX file for VDMX.
Original image from Un Chant d’Amour (1950).
James George has a very similar openFrameworks addon.
Mehmet Akten (Memo) has a static slit-scan in Quartz Composer which uses no extra plugins.
Golan Levin maintains a comprehensive catalogue of work and research using slit-scanning.