Capturing Reason for Change (Edit)

[JMG]

Before I just go ahead and reinvent this wheel, does anyone know of a Django package or what-have-you that works with "auditable" forms? I don't mean audit log--there are several of those--but what I mean is that I have an app that will consist largely of data entry forms. If someone edits information that has already been entered, then I want the system to catch that and prompt the user for a "reason for change." 

I freely stipulate that this is not tragically difficult to implement, or anything. But if someone is already doing it, or has done it, I'd love to leverage the work.

J