It’s Get Back to School time, and Inkling, the leading company reinventing textbooks on the iPad, has just won Apple’s approval for its 2.0 app. CEO Matt MacInnis calls it “the single most complex iPad app out there," and he may well be right.

It combines a 3-D rendering engine, a complex reading engine, and a full social search engine all wrapped into one, which also syncs across the devices you use to access it.

From a developer’s perspective, that’s complex.

Fortunately, from a user’s perspective, Inkling is simple to use. You tap on this, pull out that, scroll down here, and dig deeper over there.

The most striking aspect of Inkling 2.0 is the interactive social layer it has integrated across its current inventory of 50 academic titles, which will grow to 100 titles by year’s end.

Inkling intends for this social layer to provide students and teachers with what MacInnis calls “the world’s most helpful study group.”

So let’s unbundle this.

“We’re not into replicating the textbook experience,” he explains. “The textbook is an ingredient. Design is important to us; the design has to delightful to the user. We call it ‘user experience design’ that helps someone from a standing start to reach a significant learning outcome down the road.“

A big part of that experience is collaborative learning with other users. By signing in via Facebook, users can easily connect with other people they know (or don’t know) who are studying the same text.

Inkling makes it simple to share insights, start conversations, save notes, and generally tap into the collective wisdom about the topics being studied in real time. Based on a commenter’s star ratings, assessment test scores, and other metrics, MacInnis explains, Inkling “helps you find interesting people beyond the classroom, anywhere in the world, really,” who may be able to help you unlock the educational value inside a textbook.

Some of those interesting people have already been recruited by the company – topic experts whose comments (like those of professors) are highlighted in purple on the app. (An overall color-coded system let’s you recognize the status of each commenter at a glance.)

“The point here is that if a student gets stuck, he can turn to this extended study group for help.” Says MacInnis. “Old-fashioned textbook study was an isolating experience, but now you don’t have to be isolated any longer. With Inkling, you have the opportunity for collaboration, for collective learning. Who you listen to is up to you.”

As these are the very early days of collaborative learning, MacInnis anticipates that “we’ll have to hone it over time. It’s likely it will be used in ways we haven’t anticipated and we’ll have to adjust.”

And that, of course, is what developing successful software is all about.