A look at the latest trend in the MU Online market. A couple of weeks ago, Turbine announced that it was entering the free-to-play arena with the upcoming release of its MU Online Zen and Dragons Online expansion, Eberron Unlimited.

Although most people view this as a last-ditch effort to save the game from obscurity in a rapidly expanding MU Online Zen market, some also feel that Turbine is testing the micro-transaction waters with this move. This is hardly surprising as more and more publishers are getting on the F2P bandwagon.

A good portion of the US free-to-play MU Online Zen market still consists of Asian-developed games imported by local publishers, but that's certainly beginning to change. Big players like Sony Online Entertainment, NCsoft, and EA are already in the picture with Free Realms, Dungeon Runners, and Battlefield Heroes, respectively, with more in the works.

As far as popularity goes, the leader of the pack is still Maple Story, developed by South Korean company Wizet, with 87 million registered users, an estimated 10 to 15-percent of which are active players. But consider this: SOE's Free Realms recently reached the 3 million mark, barely seven weeks after it launched!

MU Online Zen will soon be embracing the free-to-play model.Of course in a free-to-play game, the number of registered users don't tell the whole story since not all of these are paying customers.

Few companies are willing to share their revenue figures, and those who do usually report their average revenue per paying user (ARPPU) rather than the average revenue per user (ARPU), which would be a much diluted figure.

Additionally, both figures are based on the number of logged in users per month, which is only a fraction of the total registered users.

In any case, the numbers seem to indicate that the ARPU on free-to-play games (which includes casual game portals such as Outspark and virtual worlds like Second Life) is generally between $0.50-$1.50, with an ARPPU ranging from $20-$30 a month.