From the website:

Multiverse lets you to build an MMOG or virtual world for less money and in less time than ever before. Multiverse technology is scalable, extensible, and highly customizable, enabling you to build your world with its own unique look and feel, gameplay, and mechanics. Our active developer community is creating a wide variety of worlds.
Make money through subscriptions, item sales, and/or advertising, and pay us only 10% of your gross revenue.
Download our client, server, tools, starter assets, and sample worlds for free and start building your world today!