Poetica was great because it allowed you to write comments in the margins of a document and have them directly attached and or inserted into document. A couple of alternative services that perform similar functions are Kaizena, Annotation Studio, and JoeZoo Express. 

Kaizena is a Google Docs Add-on that allows you to add voice comments and written comments to Google Documents. 

Annotation Studio is a platform on which you can create a classroom in which you share documents. You can create documents from scratch by using the Annotation Studio text editor or you can import a Word document or a PDF. Once you have created a document you can share it with your class or you can make it public for anyone to comment on. The best aspect of Annotation Studio is that every annotation you add to a document can include videos, pictures, text, and hyperlinks.

JoeZoo Express enables you to give feedback on students’ Google Documents by simply highlighting text then selecting feedback statements from a huge menu of options. For example, in my sample document I highlighted text then chose the category of “structure” within the structure category I then chose to tag the sentence with the comment “awkward.” When a student sees the feedback he or she will also see an explanation of “awkward” and how he or she can fix it.