The Finnish group wrote their e-book using open source software that requires programming skills but for less technically interested teachers there are plenty of simple tools available. Apple's free iBook authoring tool is one such tool and I'd like to recommend an excellent step by step guide to writing an interactive e-book by Shawn Ozbun, Create an interactive eBook for the iPad using iBook Author: THE COMPLETE GUIDE. The authoring tool is pretty locked into Apple's walled garden of course but it is remarkably easy to produce very attractive professional ebooks by following the templates and pulling in the resources you wish to use (assuming of course you have the rights to use them). have a look at the introduction film below and then go to the full guide.
Another authoring tool that works on all platforms is Widbook. More basic than iBooks but highly practical. All you need to do is write the book!