A client recently asked for a document library with a custom content type and a workflow to remind responsible users to review documents annualy. The little twist here is that they also wanted to have this document library on several sites for different departments.
Usually a workflow is connected to a list, so there was no very obvious way to solve this. Not untill I discovered that you were able to attach a workflow to a content type in the content type hub. But I struggled a little bit to get it working untill I found this neat little trick:
I followed the steps in SharePoint 2013 Online and it actually worked. I also tested that if I update the workflow after the above procedure, it actually updates the content types as you would expect when republishing them. Sweet!
BTW: here is the reminder script that I used as a SP 2010 workflow: