There have been disappointingly few apps that truly capitalize on the potential of the iPad as a personal computing platform. The criteria I would use here is simple: does the app do something that you can only do on the iPad, that you can’t do on a desktop or laptop, or even on an iPhone?

The unique app Liquid Text is one of these apps. Started as a doctoral project by founder and CEO Craig Tashman when he was Georgia Tech, Liquid Text adds a number of innovative direct manipulation features to the experience of reading documents. In fact, it’s more accurate to call LiquidText a research or working app than a reading app, as its value is in allowing the user to better use and understand the information and relationships that are most relevant to her in a text.

You can do more than just highlight information; you can make explicit and functional relationships between salient bits by simply drawing lines between them, or you can circle a chart and excerpt it instantly, or you can collapse whole passages or pages to condense content to just the essentials. This video captures some of this power in action; it’s notable that the features can be demonstrated without a voiceover and with only the briefest of text explanations, as the value of the features is powerfully self-explanatory. It’s also clear that this kind of product could only happen on an iPad.

More information at liquidtext.net.