Folia is an impressive collaboration app from the folks behind the iAnnotate PDF app. It comes on iOS, Mac, Windows and Android, and it’s a streamlined word processor that lets you mark up and annotate your documents. Better, these annotations live in the cloud, separate from but married to the document, so they persist even as you update the source files. You can also attach more documents to any section of your master file. To be honest, I can’t quite understand it yet, but it looks rad, and costs nothing.