Old way: You print out someone's work, scrawl all over it with pens and magic markers, and hand it to them. New way: You open someone's work, scrawl all over it with Argone 7 ($30), and save it as a PDF and e-mail it to them. It's all the fun of tearing apart a coworker's efforts with no carbon footprint or dead trees!
Argone 7 is a tool which allows you comment on a document and then save the commented-on file as a PDF. While some word processors allow this, a lot of documents are not stored in the appropriate format--such as programming files. Argone 7 is especially good at code comments, because it performs automatic syntax highlighting on common languages such as C++ or Java.
Argone 7 has markers, text boxes, a lot of different styles of arrows, and even large square and curly brackets. It's useful for anyone who does editing or commenting of text, and brings the paper and pencil (and colored highlighter) model into the virtual world. The trial version does not allow settings to be changed--for example, you cannot alter the font used for text annotations. In addition, I had some slight issues with determining if I had selected a particular object. Last, the trial version "watermarks" PDFs that it produces.
Overall, Argone is useful in environments where passing around Word files is not viable or useful. It allows markup of image files, for example, and creates PDF files which can be sent to non-Windows computers. It provides the flexibility of "writing on" a file while still preserving a clear data trail, as well. It is of little use in non-collaborative environments or for a single user maintaining a record of edits and changes to his own work.