Callisto

Callisto is a Java-based software application that enables you to add annotations to files encoded as UTF-8. It offers support for other encoding methods as well, uses the ATLAS data model for storing annotations, and lets you import and export inline annotations, like XML or SGML.

Easy setup and classical GUI

Since it's written in Java, you need an IDE for the programming language installed, in order to be able to set up Callisto. The app is wrapped in an interface commonly found in Java tools, which doesn't put much emphasis on looks but has as neatly organized structure.

Quickly add annotations to files

After opening a file, you can show available actions and display the cursor in the text, enable text swipe by word, press the Shift key to view annotations, or resort to a basic search function when dealing with large amounts of information.

Configure text settings and use handy tools

It's possible to toggle the orientation, customize font settings and size, select the line spacing and character encoding, as well as use tools for editing AIF references and compiling DTD tasks. As previously mentioned, annotations can be exported to file and later imported.

Evaluation and conclusion

As expected, the utility didn't put a strain on the overall performance of the machine in our tests, thanks to the fact that it consumed low CPU and RAM. It applied annotations swiftly and didn't hang, crash or display error messages in the meantime.
Although it doesn't boast a rich set of features, Callisto is pretty straightforward when it comes to applying annotations to UTF-8-encoded files. Plus, it's free.