On Friday 29 July 2011 imapsync is exactly ten years old since release 1.1!
Since November 2010 imapsync software is free, open but not gratis from its homepage. There is a special price (10€) for this 10 years old anniversary. Buying just help the author to maintain and improve imapsync.
The license is still very permissive (WTFPL), everything is permitted so you might find it gratis in other places.