Been messing around a lot lately with an MMO engine called Multiverse. It's not complete yet (closed beta state), but has some interesting potential.
The basic business model is that the tools to develop new games as well as the server are free. The company also has a single client application that is used to play any game written for their technology. Multiverse then acts as the proxy between the client and servers. If you create a new game and charge for it, they take a cut and make their money. If you charge nothing, they dont' make anything either.
It has a "steam like" system built in to allow you to download new and updated game content from servers whic I must say is pretty nice to anyone running a game that updates.
Website for the company is http://www.multiverse.net. They are doing a presentation at the Austin Game Conference and I'll be semi-fortunate to have a short trailer shown on a project I've started that's a Mars colonization themed MMO, PvE & no PvP, realistic sim set in the near future (2050 or so). Target is for entertainment gameplay, educational use and also possible NASA visualization tool or platform for collaborative development and planning of future missions. Links to info on it and a shor trailer I slapped together on their "Games Built on Multiverse" page.
Here's a screen from in-game - part of a "small" test map that is 40x40km. BTW the estimable David "Zafod" Marsh is my brainstorm buddy on this project.
[Blocked Image: http://www.marsauthority.com/images/ProjectMars_Screen1.jpg]