Hello,
We do have an XTP that does just this - it's called the Change History XTP. It has a Save button that records a history of who saved the form at what time. It also has a place where users can enter notes before saving. Each time the button is clicked, it adds a row into a repeating table with the change log.
Here's a screenshot:

You can get it here.
Let us know if you need assistance with the XTP!
Cheers!