iPad: Noteshelf is a finely polished handwriting app with loads of features including 17 notebook templates, the ability to embed and annotate photos, over 450 icons, and automatic syncing to Dropbox and Evernote.
Brainshark is a competitor to Slideshare.net, allowing anyone to upload a PowerPoint or PDF to their Web service and annotate the visuals with audio/video comments or music.
Copy editing on paper is easy: just mark everything up with a red pen. Online can get complicated. Sure, you can use the track changes feature in Microsoft Office combined with the notes function, but that's not as efficient as it could be. If you're looking for a different way, check out CrocoDoc.
SpeakingImage is an application for creating interactive images and share them with others. You can also create groups, add wikis and set different permissions to manage collaborative work