Immersive Linear Algebra (2016)
Without having looked at the text in depth, I applaud the idea here - I'm convinced the web browser can help us improve upon maths textbooks printed on paper, but there aren't many 'hypertextbooks' like this in existence (partly, I think, because most people positioned to author a maths textbook want to use latex; and most people who are able to develop a web app aren't positioned to author a maths textbook).I'm interested to know how the authors funded this, and if they have any data about the impact it has had.