I read this a few years ago - it was the first piece of multimedia fiction that I had ever read, and it inspired me to go in search of internet-based fiction, which ultimately led me to IFDB.
17776 makes use of different formats - text, video, gif, even a calendar - to tell a rather bizarre but genuinely fascinating and original story. Reading through the first chapter in particular made me feel strangely unnerved and wonder what was going to happen. I don't want to give too much away, but it's set in the distant future when human life is extraordinarily different, and is told from an unusual perspective.
Although it's relatively low on the interactive elements, the multimedia aspect of it will appeal to people interested in new storytelling formats.