Taatu, founded in Belgium in 2005, looks very much like Habbo Hotel. The similarities of visual styling and target age-group (tweens/teens: 10-19) is pretty much the first thing that everyone remarks on.
Previously available in Dutch and French, Flash-powered, free-to-play, browser-based, virtual world Taatu is now also in available in beta for English-speakers as well (all launched from a single web-page).
From a cursory inspection, I can't actually see quite how Taatu differs from Habbo, specifically.
Promises safe, managed environment? Check. Promises brands extension and monetization of content? Check. Item sales, with limited edition items released regularly? Check.
That's not to say it's not a great market. Habbo's had more than 82 million signups since the year 2000 - a very, very small percentage of the connected population of their target demographic. There's a lot of room to grow in that market, and it looks like Taatu might have a slight graphical edge.
[via Worlds in Motion]