Digress.it was a free, open source WordPress plugin for annotating texts on the paragraph level, particularly of article to book-length documents. It permitted blog-like threaded discussions to occur in the margins of the text, and was aimed at facilitating scholarly, literary, political and other discussions. While the main website is no longer available, Digress.it is still available via the WordPress plugin directory.

NowComment makes it easy to have rich, engaging discussions of online documents no matter how large (or small) your class or collaboration group. It's fast, powerful, and feature-rich: you can sort comments, skim summaries, create assignments, hide comments, highlight with multiple colors and meanings, and much more. Integrates to any LMS via LTI. Used in universities and K12 schools for the past 6 years.

Available as a web-based service and as an app for iOS, Mac, PC, and Android, Google Drive allows users to create, store, edit, and share files across all their devices. Online and offline file access available. Requires a Google account for use, but allows files from Drive to be shared with non-Google users.

Drive allows users to upload, store, and share any type of file (e.g., JPEG, MP4, JS, INDD, AI). The majority can be previewed, and many can be edited within Drive. Some files (e.g., DOCX, XLSX, PPTX) can be converted into compatible file types for editing, commenting, and more. Drive is the platform for Google Sheets, Docs, Slides, and many other approved applications. Files saved in Drive sync to all other devices, with an activity monitor that can be useful for version control (see what edits have been made and when, and revert back to previous instances if needed).

Offers both free and paid accounts, priced by data capacity: 15 GB (free), 100 GB ($1.99/month), 1 TB ($9.99/month), 10 TB ($99.99/month), 20 TB ($199.99/month), 30 TB ($299.99/month). Teams with more than five people can purchase unlimited storage for $10/user/month.