Markup eXchange

This is a pair of javascript tools designed to be run in PDF XChange (they may also work in other pdf editors, but I've not tried). One tool is a single merge too that merges all comments in multiple pdf documents without overwriting more recent changes, and detecting conflicts (ie comments simultaneously edited). The second tool will run the merge tool on a schedule to keep pdf's in sync in real time.

Background
If more than one person is adding comments to a pdf document, they either have to share a single document (but then it's locked when one person is editing it), or there needs to be a way to merge the comments in multiple documents. Other pdf software has set up subscription-based online editing to handle this, but then you need to trust your documents to their servers, and it's a proprietory solution. This is an attempt at an open source approach.